Check out this thread for an example of the post card that I use.

I'm looking for the cheapest company to get postcards printed.

One person I knew in Washington state just used to send a postcard saying you have X dollars due you.

Hello BP,I've been researching responses rates for yellow letters and postcards as I'm deciding what to send and how many to start off with.  

I need to find a suggestion on what company does a good affordable post card mailing 4x6 size range ?

Step two, choose a postcard or letter. 

I am working to acquire my first STR and I am wondering if anyone has done any marketing campaigns to find STR’s such as direct mail, postcards, etc.

My marketing has consisted of the following:•Postcards (monthly)•Probate (monthly)•Craigslist (daily)•Yellow letters•Penny Pincher AdI wish I could say one particular marketing strategy worked best but in reality, the results were mixed.

The .16 cents is for ever door direct mail, which is a post card that is dropped off to every single house in a neighborhood or zip code.

Like @Josh Caldwell said, Yellow Letters work GREAT but this came from a postcard.