Canon 300 TL - Manual (Page 23)

If the subject is out of shooting distance range, both
the shutter speed and the aperture will blink in the
viewfinder. In this case, follow the note mentioned in
the Program AE Mode.
A blinking shutter speed of 1/250 sec, warns overex­
posure in the background.
In a dark setting, a blinking shutter speed indicates
that fili-in flash photography is impossible. An ex­
posure taken in these values will result in the main
subject in correct exposure and the background
underexposed.
When the shutter speed is slower than 1/60 sec,, be
careful of camera shake.