Please, always tell the crew if you see something you're unsure of. Any crew member that ridicules you for that shouldn't be on an aircraft in the first place. After all, we do it all the time if we hear or see something unusual. Sometimes we'll know what it is and be able to reassure you, although I still always pass it on to the flight crew anyway, just in case. Other times we won't and that could be the time you save our lives. That may sound a bit dramatic but it could be that serious.
An incident that happened to me about 5 or 6 years ago. On a very cold, snowy winters morning, we were sat on stand waiting for the de-icing guys to do their stuff. It was the first rotation, so the aircraft had been there all night. After some time, the Capt made the usual PA saying that de-icing was now complete and that we would be pushing back shortly. One of the passengers called me over and with some embarrassment, mentioned that he'd not seen the right hand side being done. He was right. Somehow, the guys had completely missed one side of the aircraft. Thank God for that passenger.
Jsl