As far as I know there is no sign to indicate stalemate. Stalemate is a draw and so 1/2 - 1/2 is the correct way of indicating it.
Most of the time stalemates are obvious, but you can add as a comentator something like "Stalemate" to indicate the reader there is a stalemate on the board.
On a draw, it' entered as "1/2-1/2", is there any indication to say whether the draw is due to a stalemate or player agreement? It is possible to replay the game from the moves and check for stalemate ending, but I'm wondering if there is an indication to differentiate between the 2.
Also, is it generally considered useful to have such an indication?