If it was illegal, strippers wouldn't be allowed to dress like one. As long as you don't attempt to impersonate a law enforcement officer, you are good to go.
Yes bullet proof vests are legal. I assume if Police shirts are looking legal ICE shirts are as well. I.am sure there is some point where the impersonation of an officer laws go into effect.
If there is a guitar drawn under the word it is OK ;-))
In practice nobody much care, as long as you dont actively try to pretend you are a cop. in the same way that the national flag is often used for swimwear even though that too is forbidden by law.
excon 