Is this the only way to sign "no problem"?
While this is a very natural and common idiomatic way to say "no problem," you might also see people sign "FINE" or use a thumbs-up depending on the context. However, you should avoid signing the literal words "NO" and "PROBLEM."
Can I use this sign to mean "nothing"?
Yes! This sign is frequently used to mean "nothing," "none," or "nothing to it." That is exactly why it works so perfectly as a response to a thank you or an apology—you are literally saying the effort or issue was "nothing."
Do I have to use both hands for this sign?
It is best to use both hands for clarity and emphasis, especially when you are first learning. However, in very casual, fast-paced conversations, fluent signers might occasionally drop one hand and perform the sign with just their dominant hand.