An acorn user is a person who's inbox is constantly full. Cleaning the inbox may be a constant struggle and you never know if someone has been trying to contact you. Let them know that a way to contact you is by showing an acorn.

You feature this acorn image onto your profile/den page and a person crossing by will know that if they want to contact you, they will have to create a trade/gift using an acorn.  The person receiving the acorn may deny/reject the trade but they might know you have been trying to contact them for a message.

If you create a wrong trade, no one is responsible for your lost acorns. Please be careful when setting up your trades. 
The user who you are trying to contact may choose not to respond back to you. This is only to mention that you are interested in a conversation.