Well I'm a Pisces guy and usally I start treating a girl diffrently (diffrently) as in a good way, like; being more polite around the girl, nicer, sweeter and might change his wardrobe just to get the girls attention.
Us Pisces are usally romantic and outgoing with love but remember this don't apply to every Pisces guy, we may be romantic but at the same time shy. So you might notice everthing on top or might not even notice cause they guy is to shy to even talk to you.
The best way for you to know if he likes you, just ask him, he might say no if his shyness gets the best of him, but if he chokes answering it might be a fake no.
One more thing don't play games with him, he might just think your a nut-job.
Definitely what he said. However an easy way to know if a Pisces guy likes you is to start a relationship. A simple friendship to make him more comfortable with you. If he likes you he'll share personal information with you or even have the balls to tell you. Also watch out, Pisces are most equipped to play mind games, since we have a really good intuition and generally understand people easily. He might try to use the push and pull method so not to loose you. However the easiest way to avoid this is to be very honest about your feelings if you get the signs he likes. On a final note, never be critical to anything he tells you personal in a mean way... he won't show it too much but he'll never forget it and keep his secrets to him self