There's a lonely section on old Route 66 between Seligman and Kingman, Ariz., where re-creations of once-ubiquitous Burma-Shave signs fly by: You Can Drive A/ Mile A Minute/ But There Is No/ Future In It.

Those ads know where you're going, and they know where you've been. I thought of them this week as I was stalked by a pair of pants. Short pants, actually, and several of them.

After a few clicks, Zappos' recommendation engine went to work and started offering me the selections that people who looked at the same shorts I did ultimately bought -- a cool idea and a feature that has been useful to me in the past.

Then, I abandoned the search and did something else. That's when the weirdness started.

In the five days since, those recommendations have been appearing just about everywhere I've been on the web, including MSNBC, Salon, CNN.com and The Guardian. The ad scrolls through my Zappos recommendations: Hurley, Converse by John Varvatos, Quicksilver, Rip Curl, Volcom. Whatever. At this point I've started to actually think I never really have to go back to Zappos to buy the shorts -- no need, they're following me.

I realize I'm considered by marketing folk to be at some place they call the "purchase funnel," if you can really say that with a straight face about a $55 pair of shorts. As a media professional covering online advertising, among other things, I know why I'm getting these ads. But as a consumer I'd be creeped out by it, and definitely a little annoyed, kind of like the morning my Facebook connections started popping up on sites around the web.

It so happens these ads are some of the most transparent I've ever seen on the web. There's a "Why are you being shown this banner?" link on the bottom, which takes you to the source, Criteo, which takes you to a comprehensive opt-out page. Criteo is a re-targeting firm whose pitch to e-commerce sites is "re-engage with lost prospects via personalised banners across the internet." They charge on a per-click basis, so Zappos/Amazon are only paying for clicks, not on a CPM basis. Since I've leaved through my recommendations a couple times, Criteo earned a few pennies from re-targeting me.

The Criteo ads are keeping my shorts "top of mind," but at what cost to Zappos, whose brand is emblazoned across the ads themselves? As tracking gets more and more crass and obvious, consumers will rightfully become more concerned about it. There's a big difference between serving an auto ad to someone who's visited Edmunds.com in the last month and chasing them around the web with items once in their shopping cart. (For the record, I was just browsing and never even loaded a cart).

If the industry is truly worried about a federally mandated "do not track" list akin to "do not call" for the internet, they're not really showing it. As ads become more persistent and more customized, consumers are going to demand one place to opt out of everything, and not to have to check boxes at Criteo, Yahoo, Google, Blue Kai or whoever else is targeting them that day.

Those ads on Route 66 are retro novelty, but imagine a web where you're just pestered by persistent ads. If that's where we're headed, I'll be taking the next exit.