As mentioned, looking through it is your best bet. Remember to adjust exposure appropriately (usually 1.5 to 2 stops) for the polarizer.
Let me add that while useful, this comment taken by itself may be somewhat confusing. This does not mean that the polarizer itself will only work if aimed (on camera) at the sun. In fact, the exact opposite is the case (or perpendicular ). Polarizers are only effective in a range of angles at 90 degrees from the sun. In other words, and you can test this for yourself before ever mounting the polarizer on the camera by looking through the filter and rotating it, the light cannot be polarized effectively when the view is either into the sun or in a broad range 180º opposite of the sun. One time–honored, off–the–cuff, method to deciding whether a polarizer may be used effectively is to hold your hand up with fingers pointing towards the light source (i.e., sun) and outstretched thumb. Your thumb will then point to an approximate direction at which light may be polarized effectively by your filter.
True. But the index mark on the filters are meant to be aimed at the sun. It can be confusing if the sun is not perpendicular to the lens axis, but one can kind of figure it out. I do look through the filter, but often just use the index mark. I like the suggestion by MattKing to have two filters. I think I will try that out.
Moma don't take my Kodachrome away!
Oops, Kodak just did!