US warns hidden radios may be embedded in solar-powered highway infrastructure

Seems a little sparse on details. If the radios are actually cellular it seems it would be trivial for an entity like the US government to at least determine what SIM (and even data) any of these modules was sending.

Rather than anything malicious I'm thinking it's probably just a common module made for signs that can be updated over-the-air, and that feature just isn't enabled in the US signs.