How to differentiate...

..between JR Yamanote Line - Inner Loops and Outer Loops? Will there be a clear sign that says inner and outer? @_@

There is usually no need to. Rather, most people orient themselves based on the upcoming major stations. There are many signs stating what the upcoming major stations are in each direction. For example, if you go from Ueno to Shinagawa, you will take the train that is heading towards Tokyo and Shinagawa.

If you need to differentiate, nevertheless, you will have to orient yourself (e.g. by looking at maps) and find out on which side of the station is the inner circle and on which side is the outer circle.

Oh, I see.. I've gotten a few station maps online. I hope I get it figured out once I'm there. Thanks, Uji!!

go to http://en.wikipedia.org/wiki/Yamanote_Line#Stations

The station signs indicate the name of the next station so it is easy to see if you are on the right platform. A lot of stations have the name of the previous and the next station which makes life very easy.

Nobody here worries about the inner and outer loops, or even knows which is which quite often.

You choose the train based on the direction it is heading in- e.g. if you are in Ikebukuro and going to Yoyogi you take the train bound for Shinjuku, Shibuya and Shinagawa, because Yoyogi is after Shinjuku so trains in that direction will get you there the quickest.

The signs on the platform tell you the major stations in the direction the trains are heading- if you are going to a more minor station you just need to know which of the major stations it is near to.