The posters read: "A notice to all citizens of the United States of America. It is your civic duty to report any and all illegal aliens to U.S. Immigration and Customs Enforcement. They have broken the law." There are some phone numbers also listed on the posters.
According to this news source, neither ICE nor the Douglas County Republican Party had anything to do with this. And most of the neighbors disagree with the scattered posters, even if they agree with the general sentiment behind the message.
Most likely, these are just some generic posters that got printed off of the internet by some random person who just wanted to cause trouble (just like people did in Iowa City and elsewhere with those KKK posters). And sadly, there are too many people in this country who want to call ICE on brown people with accents.