Which is proper grammar: “Ice possible drive with care” or “possible ice drive with caution”?
As written, neither version is OK. They both require some punctuation.
Ice possible - drive with care
Possible ice - drive with caution
Of these, the first is probably better.
As has been noted, my answer assumes that this is a road sign, where brevity and clarity are paramount. For a road sign, the most important word is 'ice'; the rest is less important. That is another argument for the first version above.
If you are writing running text, then you need to do more work, such as:
The road may be icy; drive with care.
You could use a dash instead of a semi-colon. You could write 'caution' instead of 'care'. You could even treat it as two sentences:
The road may be icy. Drive with care!
If this were a letter to someone I'd say "Drive with care, there might be ice", or similar.
But it sounds like a road sign text... I don't understand why the English speaking world is so fond of textual road signs. In Norway and most of continental Europe, symbols is used for almost all types of warning signs. Texts is reserved for directions to place names, and some extra information on warning signs, etc. It's a lot easier to see a standardized symbol, than reading a text that may not be consistently written.
In Norway ice is always a possibility in the winter, but if the road is especially likely of causing slippery conditions we use this sign http://en.wikipedia.org/wiki/File:Fareskilt_15.PNG