Notice present? Hold on! (6)
I believe the answer is:
adhere
'hold on' is the definition.
(I've seen this before)
'notice present?' is the wordplay.
'notice' becomes 'ad' (short for advert).
'present?' becomes 'here' (both can mean in attendance).
'ad'+'here'='ADHERE'
(Other definitions for adhere that I've seen before include "Keep" , "Stick to, cling" , "Stick with header" , "Stick to - cement" , "Stick like a stamp" .)