If in a workshop the instructor and the whole class paints the same subject, is it appropriate to sign your painting and display it as your work. Thanks, Bob D

I have no problem signing any painting I make.
But, I do have a problem with a person then trying to sell or enter such a painting in an art show etc. as a totally original painting.
For my own records and for future reference, I sign and date almost all of my work. However, I consider workshop painting and painting made following a demo. in a book as "studies".
On the back of my "studies" I make a note to myself: Date: ----"study" at .....(workshop) or "study after......(author's name of book). This helps me remember the "lessons learned" and my level of skill at that time.