Usually, they offer up their hamlet's name as the only proof.

A corpse was the only proof they need show of their job well done.

Indeed, this was the only proof of love which had power to touch her.

The only proof we have of the fact is that this person said it.

"And surprise is our only real proof of the unconscious."

A photo is the only proof we have that this sculpture was once attached to a body.

"If death is the only proof you can understand, then here are four lives for you."

Or rather, the only proof we had, for we no longer have even that.

The only proof I need is the way in which this agreement has been negotiated.

That seems to be the only real proof- The need for love.