How do I ask the receivers of my emails to include a '-- REPLY ABOVE THIS LINE --' tag below their reply?

Question

I want to parse incoming emails (which are replies to emails I've sent) for the actual message (without the "original message" part, the signature and such). To achieve this, I would like to include a delimiter (e.g. '-- REPLY ABOVE THIS LINE --') in the reply like it is recommended in many posts I've read. But how can I ask the user's Mail Agents to include my delimiter when a user replies to one of my emails?