We have a new package of Stenso 3" letters & numbers (126 letters numbers and 54 Misc signs).  They are black and are supposed to permanently stick and be able to use on all surfaces.  I believe these date to the 1970's or so, I cannot guarentee the sticky backing is still good.  They were put out by Dennison.  Upon initial posting I have a few of these.  I did notice (shown in photo's) that it appears as though the letters have "shrunk" a tad. 

Vinyl Letters & Numbers NOS Vintage Stenso