Yes, please, either remove them or at replace them with something more meaningful. Every time I see one I have to hover over it to figure out whether something's actually wrong, and (confession time...) sometimes I even deliberately trigger a bunch of (non-)builds so it goes sunny again.

If you want to show the state of the last 5 builds, then... show the state of the last 5 builds. e.g. ynyyY (imagine unicode ticks and crosses instead)

Just my tuppence. For the record, Jenkins is amazing in how it has sparked a revolution in the CI world, and I love it, but the weather icons do wind me up somewhat.

Edit: replaced unicode ticks and crosses with y and n because they weren't showing up.