Is this some kind of secret language, or are you just high? ;D
ROLF, is an online/texting abbreviation for "rolling on the floor laughing". It is sometimes used in conjunction to with the word "copter" to mean something extremely funny. PM means private message, and URL is a Uniform Resource Locator. The best translation I can come up is is this: "There, haha this is so funny! Private Message me if you can't see them [my signature], and I'll send you a link to the picture. "
or... "i fail."