Well, I suppose everybody has ideas. The most frequent concept is that you can recognise an entities disposition or nature by it's colour; almost like an Aura, if you will. A bright or dark light around them, some people have also spoken of fantastic or nightmarish colours surrounding and covering any entities they've encountered, though there isn't any particular way to test anybody's concepts about this.
As for the whole "protection" issue, there's a few things people tend to think you can; once again, the most frequent is for you to mentally cover yourself in a "white light", which is supposed to protect you. Some people also tend to try and incorporate some forms of chakral and kundalini work into this protective ritual (of sorts), but quite frankly, I see that as an optional thing, depending on your belief in chakras, kundalini and the like. Some also say that you can simply call out the holy names of whatever deities or figures you feel represent you, or that you hold the most faith in. Once again however, take all of these answers with a grain of salt, as there isn't really an objective way to prove them.
Considering the protection works, then a "weapon" against them has already been obtained, due to their nature being restricted; that is to say, they can't harm you, therefore, you shouldn't harm them *anyway*. While I *guess* it might be possible to gain some sort of "weapon", I honestly haven't read about that *anywhere* in my time. Some practitioners of Astral Projection claim to have never seen such entities anyway; like I said, a grain of salt. ;-)