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' (both can mean an advertisement).
'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" .)