Unless the mechanics have changed (and they may have) I was taught you simply inform the WR that your belt buckle is on the line. So. I agree telling a WR they are lined up offsides would be the wrong thing to do.Different sport, but in football you will often see receivers check with the line judge to make sure they're lined up legally.
Also, different sport: in ice hockey I will caution players when contact, especially when away from the puck, is bordering on excessive, since the amount of allowable contact is only broadly defined at levels where body checking is permitted. Different animal I know, but to say that an official giving input is ALWAYS wrong, or is crossing a line is simplistic, IMO.