I've wanted more stamp capabilities like that too because anytime the customer wants to explore using them in this way I always have to shut them down.
However there is one neat trick you can use for this one - I had a project where I had to look for certain people to stamp a personal approved stamp in workflow as part of an approval process. We had each of the users create a personal stamp named ApprovalStamp and I used a search that looked for {LF:AnnStampName="ApprovalStamp", owner="User"}
But since this is a public stamp you can't search on who placed that there - Directly
There is a way that you can sort of search - you can do this:
{LF:AnnCreator="User"} & {LF:AnnStampName="StampName"}
Personally I'd love to see one of these:
Security for stamps
Ability to see who placed a stamp or annotation and being able to reference placed stamps or annotations in workflow.
If we had those two we wouldn't need to worry about Public vs Private. Heck if we just had the ability to see who placed a stamp or other annotation it would be better.
As it stands now there is a delete annotation function in workflow but it's only good in cases where you placed the annotation earlier within the same workflow. There is no find annotation function to locate annotations for it to delete. As I've learned to break my workflows apart for better management (especially with the new token passing in 9.0.2) this is becoming less useful than it already was.