for outdoors/windy conditions - i have boards glued to these . . . and on a couple i have info inside the plexiglass frame . . . and the foam board behind. also you can poke a hole in f/board and feed a ribbon thru and inside frame if you don't want to glue.
imo these make the foam board less tipsy! g/luck! http://www.concordsupplies.com/unive...FYeK4AodnWP84Q
i've also gotten these frames at tag sales/goodwill for $.25
edit . . . and when it gets real gusty - i can clamp them to the table . . . or use a rock/brick