My hand 24 hours (and a shower and several vigorous hand washings) after a Rodrigo y Gabriela concert at the 9:30 Club in D.C. My fiancee's is below.
"I am never going back to 9:30 Club. Last time, my hand stamp took 3 days to wear off!"
Okay, so no one says that, or would act that way. Economists talk about how higher prices and added inconveniences drive away some marginal customers, but a longer-lasting-than-desired hand stamp from a concert has no apparent downside for the venue. A different kind of ink likely would vanish quicker, but what incentive does the venue have for using it? The disfigured splotches make for great free word-of-hand advertising as people return to work the next day. Heck, some dork might even write a blog post about it.