Being "touched" might be something as simple as somebody moving your file from one pile of papers to another to another. Or it might mean you're a day away from approval. Truth is, it means very little other than that somebody has had their hands on your file (but maybe just to move it and not to work on it). We were touched once about 5 days after NOA1 but didn't receive NOA2 for another 4 months after that...
Click on this link:
https://egov.uscis.gov/cris/jsps/index.jsp to access the CRIS online case status site. If you haven't done so already, create a customer portfolio, and then when you log in you can see what the latest date it was updated. If that date changes then you know you've been touched.
Even though it didn't necessarily mean anything much, I checked on CRIS pretty regularly as I liked the idea of our case being looked at, or even moved! But don't stress yourself too much. As it's already been said, plenty of people have received NOA2 with no touches whatsoever.