If I may jump in to augment and fine-tune Doug's point, here in the U.S. we generally use capitalized words only for proper nouns and their derivative adjectives. If we had a political party named the Liberal party, we would talk about a Liberal politician or viewpoint. Since we don't, we talk about a liberal politician, etc. In the context of these discussions, I think it's safe to say Americans are using "liberal" to mean politically liberal, as opposed to the other dozen or so definitions in the dictionary.

Mcgrath's point has merit, if all understood Liberal to mean politically liberal it could remove doubt about the poster's intent and avoid potential confusion. Unfortunately, however, I don't think it's realistic to expect that Americans will adopt that practice. I would go so far as to venture that unless context clearly suggests otherwise, it's safe to assume that Americans using "liberal" or "conservative" mean politcally so.