For those of you new to PokerStars, cash games have a "$" sign with ALL money representation - play money games do not. Example:
$1.00 + $0.10 is a cash game (for real money)
1.00 + 0.10 is play money.

Also - same convention used on the tables (look at your bet amounts - is there a $? If so, it's real).

It can get confusing. Been there. However, if you play in a play money game for a $5 chip, you still owe (me*) the chip.

* provided I don't let Smitty beat me with a suck out 2-pair.