I had previously mentioned an article (written by Imperialforge) I utilized on making plastic banners. I found it on CMON:
The minor differences in the way I've done it are:
I used flat (non-textured) needle-nose pliers to hold the full length of the side of the banner that would connect with the pieces of tube. This way I made sure they remained straight.
I used hollow tubes, so I didn't need to drill out solid plastic rod.
Here's two of my examples:
My plan is to make a small batch of fairly generic looking banners to use as counters (mostly for captured standards and objectives) in games.