I've had this question for years but it had never been in the forefront of my mind enough to ask it. But the same mysterious formulation that I've seen occasionally all that time is cropping up on political candidate signs, and I thought I'd ask about it.
It consists of an instruction, "Text [word] to [number]." For instance, on Elizabeth Warren's campaign signs, it reads "Text IOWA to 24477."
What does this mean? What is this number? It's usually five digits long, and it's printed without hyphens, so it's not a regular phone number. What kind of number is it, and by what means do you text to it? And what happens if you do? What sort of responses do these instructions generate, and by what means do they reach you?