Welcome to the forum Jennifer. In general males have a longer tale and concave plastron (bottom shell). If you post some pics we can tell you for sure though.
Well, that should be fun to have someone hold Mr. Rogers up or sideways so you can snap a photo of his plastron and private "bits" area...
I guess it is only fair that you suffer a bit in the process since you are located in Hawaii.
Is Mr. Rogers a Sulcata? We had a new member a couple months ago from Hawaii with lots of Sulcatas on his property...can't remember which island he was on though, but we were all duly jealous.