You don't need a polerizer, I've been shooting through glass with out one for years. This applies to all reflective surfaces like automotive paint and water to name a couple. The trick is distance and/or lighting. The one rule is NEVER USE THE FLASH ON THE CAMERA.
Light on subject side of the glass
I generally try to do most of my shots like that with the primary source of light on the subject side of the glass. When the primary light source is on that side there is no reflection to speak of.
Distance
There are a few things you can do here, you can butt the lens up to the glass but you have to have either a lens with a very close focusing range or a macro enabled lens, the draw back to this is you take away any chance of alternate angles as the the lens should be flush to the glass in order to work properly to reduce access light that causes the reflection glass will deturmine what angle you can work with and is seldom good for anything other than fish.
Anther is well away from the glass, Getting away from the glass reduces the dominace of the reflection and gives you the possibility of either hiding in a shadow or composing around it. One of the draw backs is this requires longer and often slower lenses and often higher ISO.
Another is to be at about a mid range and cast a shadow over the glass where the desired subject is to artifissally create the illution that the primary light source is on the other side of the glass but this only works in overhead lighting and glass topped cases where the light can come through the top as well as the sides.
This photo was taken from several feet awat using an 85mm lens with the primary light source on the subject side.
This Photo was taken with the close focusing lens butted up agenst the glass under nutral lighting.
This Photo was taken under overhead lighting with macro equipment using the shadow cast by the lens