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You can almost universally contact a trucker by the description of his truck and/or the mile marker/highway you're on.

Almost all trailers have numbers on the back of them, huge, easy to identify. The truck might also have a company name on the side, different from that on the trailer. Check that you can identify the type/brand/make of the truck that's being contacted. Refer to truck numbers (different from trailer numbers). Something will usually catch their attention, or you're on the wrong channel.

Regardless of whether you can see a personal name printed on the truck's door/side/anything, DO NOT use it on public broadcast. You might get run over.