Tor isn't indistinguishable from normal use, that's a big reason why they want as many people using it for everyday browsing as possible.
They are trying as much as possible to minimize the distinctiveness, currently making it very similar to https traffic, and with Obfsproxy recently introduced.
So they can know that you are using Tor if they try hard enough, but not what you are doing with it, which is the important part.
edit:
The previous comment was about what a state can determine about you. Websites can just download the list of exit nodes and block access from those IPs.
Everyone could be if they wanted, but obviously it makes it look like someone else's traffic came from your home, so only a good idea if you're prepared for dealing with any complaints that could arise from that.
Tor isn't indistinguishable from normal use, that's a big reason why they want as many people using it for everyday browsing as possible.
They are trying as much as possible to minimize the distinctiveness, currently making it very similar to https traffic, and with Obfsproxy recently introduced.
So they can know that you are using Tor if they try hard enough, but not what you are doing with it, which is the important part.
edit:
The previous comment was about what a state can determine about you. Websites can just download the list of exit nodes and block access from those IPs.