A former a traffic controller told me that the speed of the Blackbird is classified so when it flies by you will see “SC” in the speed box which means “speed classified.”
He said one time when it came cruising by he put a couple of marks on his scope, which was a known distance, and timed it. After it passed by he calculated it was doing about 3,500 kts. That’s about Mach 5.
Shhhh...
Not that any ‘civie’ would believe it ;^)
Edges glow red.