a transportable sign or message holder supports and displays replaceable signs or messages . a transparent front panel of polymeric material permits a sign or message to be viewed through the front panel . a rear panel , located behind the front panel , forms a cavity between the two panels and receives and supports a replaceable sign or message . the front and rear panels are attached at the bottom of the cavity and support the lower edge of a sign or message in the cavity . a pair of suction cups are mounted along the side edges for holding the two panels together and for detachably mounting the panels on a supporting structure .