reminder

constant reminder of the need for caution

You just want key words as a reminder of the story you are going to tell

a salutary reminder

The sight of the crumpled remains of trucks and cars in the bottom of the gorge a constant reminder of the need for caution and of the treacherous conditions here over the winter months

In a reminder

just as a reminder

Have a visual reminder

serve as a reminder

Just a reminder to all the parents out there