Every letter or package I receive has 2 pen slashes on it. (like an equals sign only turned on it's side). Sometimes it's on the back but usually on the front near my address. Any idea what this means? (some big secret postal worker code, perhaps?)

Is your house/apt. number 11, by chance?

Is it every single piece of mail or one every day or on all the packages? Are you on a corner or the first/last house on a street? Do you have a good stopping place (out of the way of traffic) or a turn around just before or after you house?

It is possible that the carrier marks the mail to help remember something or it is a good place to rearrange the next section of the route to deliver.

Not apt #11

Well I have seen our carrier eating lunch in the truck in our parking lot. lol 

The markings are on every piece of mail but I'm not the first address on the street.

I just think it's weird and I'm dying of curiousity. I may have to watch for the carrier and just ask him.