If I find an abandoned/vacant property, a lot of times I will either mail them a yellow, or simply call them.

You could drive for dollars, send out yellow letters, look on the MLS, look on craigslist, auctions, For Sale By Owner, even just telling everyone you know that you're looking for a deal.

Send them a letter (not yellow letter because they are getting dozens of them) telling them you found their house to be apparently vacant.

I researched the design and did simple yellow postcards with phone number email address and website.

Send them a letter (not yellow letter because they are getting dozens of them) telling them you found their house to be apparently vacant.

Send them a letter (not yellow letter because they are getting dozens of them) telling them you found their house to be apparently vacant.

Send them a letter (not yellow letter because they are getting dozens of them) telling them you found their house to be apparently vacant.

The answers are all on this forum, and website blog.Most common method is marketing via yellow letters.  

I am slowing learning all I can about Real Estate and have heard of 'yellow letter' campaigns.

I have began incorporating different marketing campaigns such as mailing yellow letters, building websites, squeeze pages, good adwords, etc... and have began to get those calls.