Symbol on my screen

All the sudden and the bottom right corner, 2 inches from the bottom inch from the right side have a transparent or should I say, translucent looking rectangle horizontal Indirect which is about half-inch long by 3/8 tall with about an inch long black solid line across the bottom of it spaced probably 16th underneath the box anyway what is this??

does anybody know?

It started or appeared after checking some security alerts of unfamiliar unrecognized activity in my Gmail .