How do I select the number of an incoming SMS? I received some SMSes that show up both in my SMS app and in Google Hangouts; however for the life of me I can't figure out how to just copy that number (in order to report it as a spammer), short of either adding it to my contacts (I don't want to) or writing it down on a piece of paper and re-entering it (which seems just plain silly).

Googling around, it seems there are quite a few SMS/MMS applications in the wild and I can't tell which one exactly mine is (it says "Version 4.1.1", but I can't find an ID), but I would expect either it or google hangouts to have that functionality somewhere ... so what am I missing?

(the obvious things - long press, short press, double click etc. on the number do nothing, and the menus only show me options for blocking the sender or adding it to my contacts)
In Google Hangouts, if I click the contact bubble (the circle on the right where their picture would be) it brings up their contact card. If you long-click the number there, there's an option to copy it to the clipboard.

NOTE: you may need to add the number as a contact to view the number in the "contact card."