I use this simple uncluttered tool in my French Immersion class.
This sign hangs on my white board and helps students remember if we are to talk in French or English at that moment. Depending on if I want them to speak French or English, I place the sign accordingly.
I use a string to hang it and it works like an Open/Closed store front sign. Simply print this document double-sided and laminate.
Enjoy! And don't forget to provide feedback!