The signs "¿ ¡" aren't really necessaries in a informal conversation, they're necessaries just in formal writings, you don't need to use them if you're talking by chat or things like that, with a sign at the final it's ok (¿ ¡)
The true is some hispanic people don't use the signs (¿ ¡), just when it's a formal write which needs to be perfect.
In a question, you don't need to use them because the accent already says that you're making a question, like "do" and "does"
For example:
"Cómo estás?" (already start with accent "cÓmo", so you already know that it's a question)
"Qué es eso?"
"Dónde está?"
"Cuánto vale?"
Don't using the signs isn't ok... but just like in English, it doesn't matter if you write "i'm" instead of "I'm" nobody is judging you for that, forget about the signs in a informal conversation isn't so important. Just be careful when you have to write something formal.
Sorry for my bad english :P
