Not familiar with any, but in case the sticker creation system from Signal behaves like Telegram or Whatsapp, it is fairly simple to do it, specially stactic ones. Just convert the image to be within the expected canvas size (up to 512px on Telegram; don`t remember on Whatsapp) and in a format it accepts (png and webp usually do the trick). For animated stickers, it usually is a bit more cumbersome / complicated.