It’s a pretty nice place I’ve been going to. In the room/cubicle, there’s a small, empty basket. I’m not sure if it’s supposed to be for a tip, or if it’s just a random basket, to put your jewelry/glasses or something…
Any ideas?
Your not “supposed” to and Taiwanese would not leave a tip. My Taiwan friends, who are far from poor and have plenty of money to spend, always tell me to keep my money, pick up my money, don’t leave a tip…
But I do it anyway 
If you’re at the newer Thai massage places in an expat area, like Anhe Lu, then they have some experience with foreigners and may leave a basket out just because they will accept money if you want to leave it.
it’s for your wig, or your merkin, whichever you’re sportin that day.
Obviously it depends on how happy you feel after i would think? IN thailand and indonesia many massage ladies not only expect a tip they ask for one (even no happy ending).
It’s very bad form not to tip in Thailand/S. E. Asia because the masseuses are on very low base salaries. They rely on the tips to top up their income same as waiting staff in the US. No idea how it works in Taiwan but if my masseuse was Thai I’d probably tip her as well, presuming she was the real deal.