I do the same. I don't think there's a particular specification for what symbols to use for what purpose, other than that some other apps (Twitter, Microsoft Teams, etc) have particular meanings for @ and # tags.
My tags are:
@context
?person's name (especially if I've delegated something to them or it's a note of the person I need to call)
&Role
+Project Name
I find those tags are quite useful if I'm searching for a keyword and I need to filter down the list of search results (eg if I only want to find the branch of tasks under a particular +Project, rather than other notes which just happen to refer to the project name).