This function was added in SA-MP 0.3a and will not work in earlier versions!
(playerid)
playerid
The ID of the player you want to know the surfing vehicle ID of.
new surf = GetPlayerSurfingVehicleID(playerid);
if(surf == INVALID_VEHICLE_ID) SendClientMessage(playerid, COLOR_RED, "You are not surfing.");
The following functions may be useful, as they are related to this function in one way or another.