What is a MARITIME LIEN and why is Wayne Madsen mentioning this?

Can someone please explain what a "Maritime Lien" is?

The reason I ask is because in this Opinion Maker article by Wayne Madsen, he talks about a Wayne Madsen Report (his website) article from a month ago (available only to his subscribers) in which he alerted his readers to the following:

"On April 14, 2011. WMR reported on a flurry of suspicious maritime liens filed against the U.S. Department of Treasury by leading Chicago and Illinois officials: "WMR has discovered that although less than 100 maritime liens had been filed in Cook County since 1985, since March 28 of this year, 11 maritime liens have been filed in Cook County against the U.S. Treasury Department.

Such a development could be easily explained away, except when examining the names of the maritime lien filers in the order that they were filed. It is not known who some of the individuals are who filed the liens since March 28, but they are also listed:"

Go here to read the names if interested. They are not names you will recognize, but the people listed are indeed in positions of high power and influence:

[link to www.opinion-maker.org]

Again, my question is: What is a 'maritime lien'... and the obvious follow-up, what the heck is going on in Chicago with these people filing these things against the U.S. Treasury Department???? WTF????