> Or instructions on signs: ring bell for assistance, return tray to counter, close gate after use.

I have never seen this.

I have seen plenty of "Please close the gate" or "Keep the gate closed". Sometimes, the article is eluded when the noun is subject "Gate must be kept closed" but imperative + noun without an article on a sign seem highly unusual to me. It feels weird so I would definitely notice.

I have seen "ring bell for assistance" however. It's jarring everytime. I must be the strange one.