I took the time to document it a couple of years ago as shown below. I took two pictures, one showing a large gathering of liberals, and one showing a large gathering of conservatives.
Here is an example of what the liberal protesters carry when they want to make a point. This analysis was from the Antiwar protesters at The Gathering of Eagles on March 17, 2007. What you see in this picture is absolutely, 100% TYPICAL.
Here is an example of what the conservative protesters carry when THEY want to make a point. This analysis was from the Taxpayer March on Washington on 9/12/2009. What you see in this picture is absolutely, 100% TYPICAL.
Conservatives not only show wit and originality in the content of the materials they use to express themselves, but also spend time making them both readable and legible. They take pride in their handiwork, and they can do this because they have a deeper understanding of the issue at hand.
Liberals often have mass printed signs that lack originality and wit in an attempt to ensure everyone has a sign (created by someone else) that says something that the "someone else" want them to express. When you see liberals carrying their own handmade signs, they often look like this, poorly lettered and shallow in content:
I have seen this contrast over and over again. What I have concluded from this is that while liberals may have some form of conviction about a subject, it is because they want to believe something they have been told without thinking it through. Most of them have an "understanding" of an issue that is a foot wide and a fraction of an inch deep. They will doggedly stay within that framework regardless of facts and logic, and their expression of that viewpoint in their signs and banners illustrates a lack of depth, understanding and originality.