Notice group of bathers ignore (4)
I believe the answer is:
sign
'notice' is the definition.
(I've seen this in another clue)
'group of bathers ignore' is the wordplay.
'group of' indicates the answer is hidden within the clue (group of letters from the clue).
'SIGN' can be found hidden inside 'bathers ignore'.
(Other definitions for sign that I've seen before include "Public notice; portent" , "Any of the 12 divisions of the Zodiac" , "Notice; symbol" , "Indication; symbol" , "house" .)