WordNet sense 1 (a request for payment):

notification

WordNet sense 2 (a sign posted in a public place as an advertisement):

bill, card, placard, poster, posting

WordNet sense 3 (the act of noticing or paying attention):

observance, observation

WordNet sense 4 (discover or determine the existence, presence, or fact of):

discover, find, observe, detect

WordNet sense 5 (notice or perceive):

mark, note

WordNet sense 6 (express recognition of the presence or existence of, or acquaintance with):

acknowledge

WordNet sense 7 (make or write a comment on):

remark, comment, point out