...but every driver I've ever talked to -- I've tried to leave a tip that way more than once, because, you know... One isn't always at one's best when one has to take a taxi home -- they all say that doesn't work, and that I just won't get billed that extra amount. Which has turned out to be correct in those cases where I'd already got around to adding something on as I was signing the slip, AFAICR.

I'm thinking maybe that's some stone-age remnant on the slips, a relict of how the system *used* to work -- but they don't do that any more, because of the risk of fraud (by the staff at the selling establishment).

Anybody know better?