What does the "RP" rating icon mean?

The "Rating Pending" symbol is only for use in advertising and marketing materials released prior to the assignment of an ESRB rating. Publishers will sometimes place advertisements for a game prior to it having been rated, and in these circumstances they may use the "Rating Pending" symbol in advertisements for that game until a rating has been assigned. Once a rating has been assigned, however, all ads placed thereafter must carry the ESRB rating. A game never actually ships to stores with a "Rating Pending" symbol on the box; all final product released must display the rating assigned by the ESRB.