Noun
dead giveaway (plural dead giveaways)
(idiomatic) Something that discloses, usually unintentionally, a fact or an intention.
That disguise is a dead giveaway! Choose something less obvious.
Even at the United Nations, where legend has it that the building was designed so that there could be no corner offices, the expanse of glass in individual offices is said to be a dead giveaway as to rank. Five windows are excellent, one window not so great. Enid Nemy
And then I would realize that would be a dead giveaway to my new life, so I would rewrite, “So then I went to bed.” Source: Internet
Although photographs had a limited perspective on the craft, Cinema Blend called it a "dead giveaway" that the ship is an A-wing. Source: Internet
The Reference and Change bits of the Storage-protection Keys, however, were labeled on the rollers, a dead giveaway to anyone who had worked with the earlier 360/67. Source: Internet
I'm a huge Hitchcock fan, so I was quickly able to figure out what was going on (the title is a dead giveaway, pardon the pun), but it was fun to watch how it all unfolded. Source: Internet