I've noticed over the years that more people don't care about the signature and want it covered with the matting. About 50-50 now. The biggest reason is that the white border distracrts from the art and they don't care about the signature just the overall feel of the art when I'm finished framing it.
But if you want to sign it, then, yes the preferred place is on the front.
As for the comment by jdyrek, let me refine that... it gets t-hinged to the board BEHIND the art, not to the back of the mat. No one with any time in framing would t-hinge art to the back of the mat.
The reason for that is in case someone opens the package and lifts the mat, there is more chance of the art being damaged than if it is hinged to the board behind it.
Another reason is that if the mat has been damaged, you only need to remove the old mat and place the new mat in the same place ... no need to do a complete remount of the art. If the new mat is cut properly, it will realign with the art.