Let me share with you this email that I received this morning,
Subject: Why Gentile-themed Mazuzah covers?
Please explain your reasoning for carrying Mazuzah covers that are themed with things such as cartoon characters, dolls, etc. What are the Kosher requirements for Mazuzah covers? You say that you sell only kosher items because you sell only items you "believe in". To me, this implies that you believe in the sanctity of the items you sell. Are Shrek, Popeye, etc. acceptable to God for covering sacred writings?
--Shannon (a Christian Gentile who prays for the Hebrew people, as the Bible says to)
Here is what I replied:
The Mezuzah cover has no holiness at all in Jewish law. It is simply a practical item to protect the Mezuzah scroll. You can decorate it however you like. Personally in my home, we do not use Mezuzah covers with characters etc (nor do I allow my children to play with such characters at all for that matter). But I don't see any problem with it. In fact, I have had many situations in my store where a Jewish person who is not religious at all and otherwise wouldn't bother to put a Mezuzah on their child's door, purchases one because the child falls in love with one of the character covers.
In short, the way I see it is that if it is permitted by the Jewish Law, and it brings some Jewish people to fulfill a commandment that they may otherwise not do, it is a good thing.