No. on a sunscreen bottle

SPF

Think of the three-letter rating that measures how well a lotion protects your skin from UV rays—often followed by a number like 30 or 50.

The clue refers to the standard label you see on sunscreen bottles that indicates how well it protects against UV rays. "No." is short for "number," and the number on sunscreen is always followed by "SPF," which stands for Sun Protection Factor. It’s a straightforward abbreviation clue—no wordplay, just a common term you’d recognize from everyday products. Think of the SPF rating like 15, 30, or 50 printed on the bottle.