Stand facing the player, hold your hads out and say
"rings, bracelets, (move a hand up to your collar) necklaces, (hands up to your ear lobes) earings and studs all off? (gesture to turn around) boots please, thanks"
Starting at their hands looking up to wrists, then neck line, ears, then thy'll turn and flick one foot, then t'other.
If you do the action, and you state the action you want them to do, naturally humans will follow the visual actions and audible command they hear. Hence puting your hands out
If you find anything point it out that it needs to come off, then do a David Cameron - Move on to the next player quickly. This does not allow you to get into conversation with them as if they want to protest - you're now already doing the next persons kit. When don the next, come back to him as see if it has been removed. If of, all good, if not be confident - it needs to come off please - you're not coming on till it's off, and move to the next player.
There is a certain amount of arogance that is needed such that they understand that you want it off, and there is no exception. By buysing yourself with the other players you are shoing that you know you have a job to do, and will do it regardless.
NB if a keeper has already got his gloves on, you are not going to be on his Christmas card list if you demand him to take them off to check for rings. You can always gently squeeze over his fingers if you have doubts.
and in womens football be even more vigilat - nose rings, studs in other parts of the ear, Trachus, Conch, Rook etc.
Oh and you'll always get the "what about the one in my c#co / nipple / belly button (and once a cl!t from a lady) piercing". how you wish to anser that is up to you""