It is if it appears to favour one religion above others, as many feel it does.
I find it ironic that none of the Christians here seem to know that the traditional Ten Commandments were not the ones that we see on monuments and other religious displays.
What Moses actually supposedly brought down according to the Bible was this:
"17 Don’t make metal images of gods.
18 Don’t fail to observe the Festival of Thin Bread in the month of Abib. Obey me and eat bread without yeast for seven days during Abib, because that is the month you left Egypt.
19 The first-born males of your families and of your flocks and herds belong to me.
20 You can save the life of a first-born donkey by sacrificing a lamb; if you don’t, you must break the donkey’s neck. You must save every first-born son.
Bring an offering every time you come to worship.
21 Do your work in six days and rest on the seventh day, even during the seasons for plowing and harvesting. 22 Celebrate the Harvest Festival each spring when you start harvesting your wheat, and celebrate the Festival of Shelters each autumn when you pick your fruit.
23 Your men must come to worship me three times a year, because I am the Lord God of Israel. 24 I will force the nations out of your land and enlarge your borders. Then no one will try to take your property when you come to worship me these three times each year.
25 When you sacrifice an animal on the altar, don’t offer bread made with yeast. And don’t save any part of the Passover meal for the next day.
26 I am the Lord your God, and you must bring the first part of your harvest to the place of worship.
Don’t boil a young goat in its mother’s milk."
Very few Christians would recognize those and since the last one amounts to a ban on cheeseburgers they probably would not be very interested in posting it on the wall.