http://www.eccie.net/showthread.php?t=149995 This is a great step-by-step guide.
I used to manage a massage parlor.<br />
Tip first, then ask!
If you are just suspecting it they probably don't. They like to make it abundantly obvious in my experience... there is no way you would be asking this question if this was one of those places that I've ever seen.
Its not so much like there is a sign - its just patently obvious by what people do, wear and say. He should flirt with this girl about it if he is not sure... at least its safe then.
If he is getting some kind of real massage to begin with I'd be surprised if its one of 'those places'.
I don't encourage this sort of thing in anyway. It can be soul destroying...
I suggest that you phone and ask about extra services( this is the correct question and if receptionist is asking what kind of extra services, you can ask straight away if they provide also happy ending massage), is better to ask by the phone before you book a session, to avoid time wasting for you and for massage therapists.
The towels you are lying on smell like *********.