That includes flyers, business cards, postcards, letters, etc.

Of course, the method of reaching them (direct mail post card vs letter) may make a big different in addition to the message. 

Once i locate owner names i skip trace the owner find their current address and phone number, I usually like to just give them a ring but often times ill follow the phone call up with a yellow letter or postcard if i cant get them on the phone.

Still in process of Advertisement, printing, Buyers list, Seller post cards, etc.

I also send them a postcard asking them to go to my web site and sign up for my wholesale buyers list.These are real players who are buying today.

Zip letters yield a higher response rate compared to postcards (higher quality leads) but are more expensive.

My gut says to spell out the specific property address, but a lot of online printing services (Costco for example) don't give you the options of merging a mailing list with the mailer to create tailored postcards and letters for each owner on the list.  

Do you use a postcard mailer or a personalized letter to the homeowners? 

I haven't used it yet but it claims I can take a picture of it and it will "research" the property and find owners' contact information and send a direct mail post card.

If anything, send them a monthly postcard in case they eventually decide to sell your name will be ingrained in their mind.