Matt Vayda wrote:How can one assure that one does appear as a number in some system?
A valid question indeed. Disclaimer: I'm only a semi-industry insider, but I'm pretty sure that most of what follows is true. 
Allllll righty then.
Hulu, Amazon, Netflix, iTunes, virtually any online viewing portal... these views DO get counted. If you watch content via any of those systems, your view is recorded in a database somewhere. And those tallies do have value. However, it's important to remember that none of those views are of any interest to a TV network.
TV networks (for the most part) do not own the shows they air, they are licensing them from the actual owners. They license them for one reason alone - to draw viewers so that those viewers will watch commercials. The more viewers, the more the networks can charge for ad minutes. If the ad minutes sell for more than the show costs to license, everybody's happy.
The revenue from all those ancillary markets like Hulu and iTunes does not go to the network that airs the show - it goes to the actual owners of the show. Which is a nice bonus for the owners, but contributes nothing to a network's interest in keeping that show on the air.
It's possible that a low-rated show with crazy-high online views could give the owners some wiggle room with their network - "See, our show has a million more fans than you think, we just have to get them to watch it when it's on your network!" But exactly how do you get those fans to switch to watching the show on air? That's the hard part.
More likely, high online views might signal to the owners that their show has a market, just not a market on air. The owners might decide to license the show to the network at a loss, in hopes that they will make back the difference with those online revenues. Maybe. Again, it depends on all the specific factors of that particular show.
A good recent example is Community - when it went on hiatus its ratings were low and it was deemed to be in trouble. While it was on hiatus, an unusual thing occurred - all of its episodes suddenly appeared on Hulu. Not just the previous six-or-so episodes that had aired, which is the norm, but all episodes for all seasons. Very unusual for a show still on the air. I don't know for sure, but my guess is that it was a very clever roll-of-the-dice by the owners of the show.
Remember, it's not the networks that evolved that last-six-episodes-online standard, it's show owners. Putting all your episodes online while a show is still on the air is likely to reduce your DVD and syndication sales potential (and again, that money goes to the owners and not networks). I'm guessing Community's owners opted to try a different idea - let's put them all out there during the hiatus, and give people a chance to discover the show and get completely up to speed with it before it comes back on air. In other words: Let's trade some of that future back end in hopes of buying ourselves another season now.
At the same time, there was a lot of grassroots campaigning from Community fans that helped raise awareness of the show - and the availability of those back episodes on Hulu made it possible for anyone to check out the show to see what all the fuss was about. And voila - when Community returned from hiatus, its rating were measurably higher, right from the first episode. All those Hulu views meant nothing to the network - but the increased ratings did, and now Community is probably a lock for another season.
As with all things in life, there are more factors at work than just the ones I mentioned... but I think Community is one of the few examples of a "Save ___" campaign that actually managed to move the needle in a meaningful way.
So as for your original question - I can only think of one answer, and it's not a particularly good one. To truly help prop up a low-rated show, you have to convince one or two million new people to start watching it.
Because that is the only thing that matters to the network. You can write all the letters you want to the network saying "I love the show, I watch every week, please don't cancel it." And that's nice and they will be happy to hear it... but their problem isn't with the people who watch the show. They need MORE than just the people watching already. (Similarly, no study has yet proven a link between plastic dinosaurs sent to network offices and increased viewership.)
So it'd be great if you had a half-million Twitter followers or something, because if you said to your half-million followers "OMG U have to watch Fringe it's awesome #seriouslydoit" you might actually make a difference. Because statistically somebody in that half-million could be a Nielsen member, and now we've got the potential for actual results. Wil Wheaton may have kept Eureka on the air these past few seasons singlehandedly, just by tweeting about his appearances on it.
(Not surprisingly, there's already a whole new industry just for this - people with popular blogs and Twitter feeds etc, are constantly approached by advertisers who pay actual money for one Tweet a la "Just tried the new Starbucks Fruity Slushpile... yummy!" Ka-ching.)
But if you don't have a million Twitter followers, I guess your only choice is grassroots - get the word out however you can, to try and find new viewers for a show that needs them. Get the word out far enough and there WILL be Nielsen viewers in the crowd, and voila - one of them watching will represent all those other new viewers you dug up. That's how statistics work.
There might be other ways to get the job done, and maybe someone will come up with one - just always remember that if your goal is to help a show stay on the air, your only weapon is to convince people to watch it when it's on the air.
In the meantime, there's certainly no harm in watching shows online, and at the very least you're telling the folks who made the show that at least ONE person out there likes it, and you're putting a couple of pennies in their pocket at the same time. The only useless activity is pirating, which neither impresses networks nor compensates show-creators.