squares! love that.
squares are usually missing characters in a font, which means it could actually be any differetn number of binary 'characters' (values).
the long and the short of it is, you should probably treat the binary data as all numbers and not fool with strings. figure out the exact character value of what you're after, then you can use strpos, stristr, explore or whatever with chr().
hope this helps.
good luck,
eric