twirling baton n.
[PLATO] The overstrike sequence -/|\-/|\- which produces an animated twirling baton. If you output it with a single backspace between characters, the baton spins in place. If you output the sequence BS SP between characters, the baton spins from left to right. If you output BS SP BS BS between characters, the baton spins from right to left. This is also occasionally called a twiddle prompt.
The twirling baton was a popular component of animated signature
files on the pioneering PLATO educational timesharing system. The
archie Internet service is perhaps the best-known baton
program today; it uses the twirling baton as an idler indicating
that the program is working on a query. The twirling baton is also
used as a boot progress indicator on several BSD variants of Unix;
if it stops, you're probably going to have a long and trying day.