i.e., violators might blow themselves up.
This is a warning sign off of El Paso's Trans-Mountain Highway, at the edge of Ft. Bliss' Castner Range. The Army tried to clear the range, but who knows what they may have missed. I have hear reports that you could hear explosions when there were brush fires up there. These stories may have pre-dated the clean-up. (ref: my previous post on the subject)
P.S. - check out the snow in EP!