Bull's Eye (postage stamp)
WordNet
noun
(1) Something that exactly succeeds in achieving its goal
"The new advertising campaign was a bell ringer"
"Scored a bull's eye"
"Hit the mark"
"The president's speech was a home run"
(2) In target shooting: a score made by hitting the center of the target
"In repeated sets of five shots his numbers of bull's-eyes varied"
(3) The center of a target