You can do this with invisible tokens. Make a fully transparent, 70x70 PNG and upload it. Create a character named PC X's Visual Cue (or something to that effect) and make it Editable and Controlled by the associated player but do not add it to their journal. Give the token a 0 aura in a color (maybe matching the player's color next to their name), and make the token the default token for the Visual Cue character. Repeat with a new character, token, and aura color for each player. When you need the visual cue, you can drag the Visual Cue character from the journal to the correct spot, and the player will be able to see it.