It's a base64-encoded WOFF (Web Open Font Format) file. All that unreadable text is the font. Instead of having the actual WOFF file on a server somewhere, Roll20 uses a data uri with the encoded file to load the font. If you put that code in the address bar, your browser will download the WOFF file, but it has to assign a default file name, since there isn't a file name included, which means you need to rename it to add the extension. Most computers aren't by default set up to understand WOFF outside of a browser, hence my suggestion for a WOFF-to-TTF (True Type Font) converter. TTF is the most common font format for both Mac and Windows. You could then install the TTF and make use of it in any program that reads your computer's installed fonts, like the text tool in a nice image processor (GIMP, Photoshop, etc.), and changing the image size/color would merely be a matter of changing the font size/color.
