This is an example of a Silly Putty envelope used around 1974 -76. My dad is (via this envelope)sending me a photograph. In his (undated) letter he asks about my son (his granchild, Troy) and says "I'll have to send him some Silly Putty. I just never think to do it".
The handwriting is my father's. I have always associated the trademark, however, with my father's writing. I'm not sure who did the trademark or the design.