The E5c used to be manufactured by Westone. They are virtually identical in form factor / shape of the earpiece. The E5c have a thicker cord, memory cable around the ear, and have a higher impedance and different sound than the UM2. They both have the crossover built into the cord. The UM2 cord is lighter and braided, and slightly shorter. The angle of attack on the tip tube is less than the e5c so some people find them more comfortable.
Shure gets the edge on warranty as Westone only offers 90 days for manufacturer defect. I have never had any trouble with mine, so I have no idea what their replacement policy is like but I have heard that Shure offers replaecment for a very fair price after their warranty runs out. Westone used to have the edge on price, but from what I have seen, deals on the e5c come very close to the msrp of the Westones. I paid roughly $40USD less than msrp for my UM2s.
I cannot compare the sound as I have not heard both.
Nobody is going to be able to tell the difference between their look unless they get to sit them side by side and look at them. Their fit will be similarly nearly identical and, unless someone is right up in your face, they won't be able to say for sure which you have.