Attachments in the File Exchange space have custom JMP icons, but attachments in the Discussions space don't.
For example here's an image from Thickness Phase I:
Here's an image from Generating random data based on correlation matrix:
The custom icons are called in this theme file /template/docs/presenter/presenter-attachments.ftl but I'm not sure why that's not being picked up across the site.
This thread at The Peak may shed some light (or it might not. ;-).
