And there's a far more obvious reason for Martin to run from Zimmerman - namely Zimmerman was obviously staring at Martin, and had pulled over his car to the side of the road in order to do so.
Which gets us back to the central point - when Martin was standing around, he was suspicious. When he was walking around, he was suspicious. When he ran from a guy who was strangely staring at him, he was suspicious. It seems like there was absolutely nothing he could have done, that would not have been seen as "suspicious" by Zimmerman.
I agree 100%. Unfortunately, the burglaries made for a situation where people just seemed suspicious.