From what I know ending verb in え makes it sound rough and very casual. I checked in tangorin.com online dictionary - it's said there it is actually a noun. To me, though, it looks like a rough intransitive version of 止まる. Why 止まれ?
止まれ is the imperative form, so it's basically equivalent to "Stop!".
I'm not sure where you get "rough intransitive" from. 止まる is intransitive already and 止める transitive.
Although the imperative is usually considered too blunt for speech, the 止まれ road sign is usually the best example for a standard use of the imperative.
The imperative for 五段 verbs (e.g. 行く, 待つ, etc.) is formed by sending the final kana to the え-row (e.g. 行け, 待て, etc.)
The imperative for 一段 verbs (e.g. 食べる, 見る, etc.) is formed by appending ろ to the "ます-stem" (e.g. 食べろ, 見ろ, etc.).
As Earthling says 止まれ is the imperative form, so it's basically equivalent to "Stop!" In this context the imperative is not "rude", it is quite simply an order.
This also explains why the て-form is not required.
止める is transitive. You would use it to say stop the car, but as in English, it is normal to refer to the person, just as you might say to a taxi driver in either language, "Turn left here and then stop on the right hand side "/「ここで左へ曲がって右側に止まります」.
(Note: To be precise, the English verb for stop can be either transitive or intransitive but it is important to grasp that, for whatever reason, intransitive is the norm in Japanese and even in English speaking countries when you see signs on the motorway such as "Please drive on the left" or "Please drive slowly" (etc), I take them to be intransitive because it more pressing.)