I have noticed some members put exclamation and question marks in the notation of their diagrams, (for example: 12. Rd4!?). I haven't been able to figure out how to do so myself, and I would like to. 

To be clear, I want this not in the comments, but in the bolded move notation above them.

there is a drop down menu for it

No problem, I saw it.

Thank you!

...how does one find/make those diagrams? Is there a plug-in for Firefox or Safari or something?

first icon above where you type

Ahhh, good to know. Thanks!