You don't really need to make them that small. The Ritsu sig for example, I think it was better with bigger size in pixels. I tried it quickly, and used the Save for Web on PS and got it to ~48000 bytes and can't see really any difference in the quality ..
Anyway, not bad sigs in overall but they're all missing a border... Simple 1px black border would do the job. The K-On has border but it's so thick it feels like it's part of the actual image ..
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