The blog post on which I relied for a copy of the icon appears to have been incorrect. The correct photo, according to AP and Yahoo! News Photos, is this:

I can't read the text, but this site, which discusses what appears to be this icon, independently of the Slidell controversy, reports that the text corresponds to John 7:24 ("Judge not according to the appearance, but judge with righteous judgement") and Matthew 7:2 ("For with what judgement you judge, you shall be judged"). This is indeed more courthouse-related text than what I understood the quote to be earlier. [UPDATE: The ACLU of Louisiana was kind enough to send me a more readable version, and Sasha, who knows how to read Old Church Slavonic -- which differs enough from standard, even pre-1918 standard, Cyrillic Russian that it requires special skill in reading -- was kind enough to transliterate it into Russian. With this, he and I can confirm that the text is a combination of John 7:24 and Matthew 7:2.]

Still, the bottom line seems to me to remain: To the extent the text matters, it's New Testament text; to the extent the text should be ignored, since the overwhelming majority of observers won't understand it, it's apparently a depiction of Jesus. In either case, it seems unconstitutional even under Justice Scalia's proposed test for a court to display the work in this context, as a standalone work in a court house with the caption "To know peace, obey these laws."

UPDATE: Thanks to commenter Paul Lukasiak for a pointer to the picture as it appears in context:

The recent posts about the picture of Jesus in the Louisiana courthouse, with the inscription "To know peace, obey these laws," has again brought up some of the arguments that the ACLU is anti-Christian or anti-religious.

There is much I disagree with the ACLU about, including about the Establishment Clause. (I've criticized the Executive Director of the ACLU of Louisiana in particular here.) But I should note that the same ACLU of Louisiana sued on behalf of a Christian anti-gay picketer, rightly argued that the First Amendment protected his speech. And of course ACLU chapters in other states have likewise fought for Christians' rights. So one can certainly fault the ACLU's position on church-state, religious freedom, and religious speech issues; but one should do so without incorrectly caricaturing that position.