Hola Thea,

No, without context we can't. But we state in the lesson that we never use El Presente de Subjuntivo after por si/por si acaso, and in this specific question you have two options to choose one: 

Escribe la dirección del hotel, por si ___. 

(Note down the hotel address in case you forget.)

 se te olvide | se te olvida

One is showing the present subjunctive and the other the present indicative, so the only possible correct answer is the second, the indicative.

I hope this clarified it.

Saludos

Inma