[Source:] We must first consider whether this was intended to be a promise at all, or whether it was a mere puff which meant nothing. Was it a mere puff? My answer to that question is No, and I base my answer upon this passage: “£1000. is deposited with the Alliance Bank, shewing our sincerity in the matter.” Now, for what was that money deposited or that statement made except to negative the suggestion that this was a mere puff and meant nothing at all? The deposit is called in aid by the advertiser as proof of his sincerity in the matter — that is, the sincerity of his promise to pay this £100. in the event which he has specified. I say this for the purpose of giving point to the observation that we are not inferring a promise; there is the promise, as plain as words can make it.
call something in = 5. Require payment of a loan or promise of money:
Definition 5 seems wrong; how does it make sense for the advertiser to require payment of his own deposit?