SAN LUIS POTOSI to MEXICO CITY -- Along the highway to Mexico City, placards every few miles advertise the availability of "tuna" -- which puzzled me, till I put my brain into Spanish mode and figured out the vendors were selling not tuna but prickly pear or cactus fig. They also sell peaches, as well as fresh strawberries and cream. I tried the last of these, with no ill effects (yet).

"Tuna -- Duraznos -- Fresas con Crema." These were the most common homemade road signs. I liked these official ones as well:

Please do not Leave Rocks on the Highway

Unnervingly, to guide trucks toward safe areas when they lose control:

Vehicles without Brakes Follow the Red Line

My favorite of all:

Signs are Here for Information -- Do not Destroy Them

Miraculously, this last one was undefaced.