When to use articles and when not to? [duplicate]

Possible Duplicate:
Please use other door?
Is "Stick no bills" correct English?
“train approaching”
What's with syntax in newspaper headlines?

Well, I know the basic rules about using articles, but this is a different case. On pedestrian traffic lights there are signs like:

Press button. Wait for signal.

Why aren’t there any articles before button and signal here?

Solution 1:

It's done to make it concise and sound like an instruction. eg

Break egg and put in bowl.

You assume that the article the is used, as in "Break the egg and put it in the bowl." In recipes, ingredients are mentioned before the instructions, so the article the is more appropriate.

To make the instructions concise and easy to read, this implied article is omitted.