Adding a tick (checkmark) icon

[sobyrne]

I use pdf-tools to add comments and to mark up student reports and assignments. It's great, and very convenient. One thing I really miss, though, is the ability to add a check mark (or tick) to the document to indicate something a student did right. Is it possible to add the ability to incorporate such an icon into the listed types, like the caret or the circle? It's not listed among the listed types. How hard would it be to add an icon like this? Is it something an end-user can do or must it be incorporated into the package itself?