The information is at least available on the web, even if you have to hunt for it. But there’s no indication on the email.
If we’re in agreement that some kind of indication is required then there are only two things to resolve:
- Position. (Above or below the content of the message?)
- Design. (How large, how subtle, etc.?)
For group PM, I like the design @DeanMarkTaylor suggested (including the positioning):
I suggested the more subtle approach at the bottom as being less noisy, but perhaps noisy in this case is a good idea.
Incidentally, maybe [PM] is not the correct term for the email’s subject. That’s a bit confusing as well.