*actually takes the time to test in creative mode*
Huh. You're right. I could've sworn that some modded added a way to get a sponge that erases signs... but none of the sponges in my slightly modified Infinity instance do. I guess that functionality was in some other mod that wasn't included in that pack.
You might want to try vanilla Item Frames or Bibliocraft chest labels. While you can't type on them, you can use them to display items, such as whatever your bees produce.
If that doesn't suit your needs, I recommend investing in either Bibliocraft fancy signs (which are re-writable, as I just found out- shift-click with an empty hand to open the GUI) or a cobalt TiCo axe.