Actually he could not use the name "Prince" during that time because the record label 'owned' it and he was suing them for breach of contract on a money matter. The record label's attorneys got an injunction against "Prince" using his own name! And...Prince was banned from talking about the case to the public. So, as a "$%^& You" to the label he made up the symbol.
Thanks to you and everyone who explained this to me. Guess I had forgotten the history of the "name change."