10
“Don't tell anyone until the prize is confirmed”
The request that has no innocent explanation.
Sometimes framed as security, sometimes as rules, sometimes as protecting you from people who will ask for money.
There is no version of a real prize promotion that requires secrecy from your own family. If anything the opposite is true: promotions want publicity, which is why they ask winners to sign a release allowing their name to be used.
A request for secrecy is a request to remove the one thing most likely to stop the fraud, somebody else hearing about it and saying, hang on.