Visible through the cab window? This I doubt. I'm in and out of cabs all the time, and while you might be able to tell if someone's probably (probably... but maybe reading their track warrants, instead!) ...reading a book or newspaper by the way they're slouching, determining that they're texting on a device that's maybe 5 square inches would be impossible from outside the cab window from the ground or platform. Obviously, the electronic time stamp would be the only reasonable way to tell.