I think it is so funny that some traffic signs say "Slow", instead of "Slow down" or "Drive Slowly". My friend says it's the same as "Stop" or "Yield." I disagree. I know that some imperative sentences are one word, but I think I don't think saying "Slow" alone is correct grammar. Am I wrong?
I agree with the purpose. It just makes me laugh. I am unique like that.

hmm I think 'slow' by itself doesn't mean much. a 'stop' sign means stop but slow (to me) could mean:
1- slow down
2- u are too slow
3- I would be thinking "how slow should I slow??!?!"

:]

nope ...

You're right that it sounds funny to say 'slow' by itself - its not a proper sentence at all!

But on road signs, the priority is to get an important message or warning across to people who are travelling at speed. The reason it says 'Slow' instead of 'Slow Down' is *NOT* to save money, but because the driver will register/read one word more quickly than two. So signs with a single word are the most effective and therefore safest way to get the message across.

You are correct. You need a verb and a noun or pronoun to have a complete sentence.

In terms of a road sign that's done to save money. You're correct that the grammar is wrong but everyone knows what it means when they see it and it saves on the cost of producing the sign.

it depence

I haven't thought of that before...I guess the signs can just say slow instead of slow down because it's kind of a given since people don't use the phrase Slow Up and the signs on the side of the road that say "slow" are meant for drivers on the road so it would be redundant to say Drive Slowly.
But you have a good point!

Well mostly the government wants to save money, and thinks that one word will be enough for the citizens to know that they have to slow down. You are right that it is grammatically wrong.

Road signs are designed to be read quickly as the car is moving and the driver shouldn't be distracted for too long.

Since "Slow" is a verb (to reduce speed) then it can be a sentence. The subject is an implied "you."

Here in the US, we have signs that say "Slow Children." I always thought that it was a shame that there were so many retarded kids in our town until someone told me that there was an implied comma between the two words. It should read "Slow, Children" and have both an implied subject, but an implied verb, too! It means "You Slow Down, There Are Children Here"