No. Master Hub Doubling is not considered a true Doubled Die. 1972P Lincoln Cents are a good example.
I found a nice grade 72 with the notching in the D and what appears to be a separation line running up the E. how do I know if what I have is a result of this?
@bryantallard checkout this site for the Master. The comment about the E leads me to think what you have is from the known Doubled Master Die, that has a tripled 'E'. I've seen this on many examples. Go all the way to the bottom of the page to read about it. http://doubleddie.com/384301.html
It's good for someone like you to familiarize yourself with the PUPs of these and simply because there SO many of them out there.
i noticed in the read that dchjr linked that it talks of 60-70% of all 72's have this doubling. also mentioning that it is listed as MD-5-O-I+II but people would leave the MD off and just refer to as 5-0-I+II. which is deceiving. if I were to actually waste my time selling one I would list it correctly and let the buyers decide how bad they want it for their collection. can't see getting more than a couple bucks for it.
If you could get even a few dollars for one listed honestly, all the power to you. Just be sure to be exceedingly clear in addition to the referenced number so that there's no misunderstandings. Hell, if willing to roll the dice it may be worth offering in a properly labeled flip as an example of master doubling. Who knows... it may be worth it for someone new. Good luck either way.