Actually, I don't have much faith in many Americans being able to figure that out ... It seems that they need things spelled out in words. Like "SPEED LIMIT" and the number ... not just a red circle with a number inside it! "What's that?" LOL! International road signs are the other way around, all symbols and colours, of necessity since there are so many languages.
Re the above post about maximum and minimum speed limits ... Red circle with white background, and some symbolic/numeric restriction inside it, is a "don't do this" or "don't exceed". Blue sign with white something inside it is a "you must do this". Black circle with a diagonal, possibly with some symbolic/numeric restriction inside it, is a cancellation of the restriction. If there's no symbol inside it, it is a cancellation of all restrictions (and resume the default restrictions for the type of road that you are on). If that sign is seen on a German autobahn, it means YEEE-HAAA.
The Germans are extremely diligent about ensuring that every "begin restriction" sign has a corresponding "cancel restriction" sign at the other end of the affected zone. The Italians, not so much. Mexico ... forget it - which is probably why Mexicans treat regulatory signs as background scenery.
Americans would really be confused by this European concept: The sign indicating the name of the village that you are entering, also puts into effect the default urban restrictions, including the default urban speed limit, and the sign cancelling the name of the village as you leave it is also a cancellation of the urban restrictions (and resumption of the rural restrictions including the rural speed limit).