A replacement lid that fits a Sharpie, made in the form of an historically accurate medieval mace, being modelled on one of the maces in the Royal Armouries Collection of Leeds, England. It prints fine, vertically positioned, without supports but I recommend using a brim as the footprint is very small.
I haven't had a chance to use this model for a long time so, while the fit certainly feels airtight, I cannot guarantee your pen's ink won't dry out at some point (I will update the model if I get reports of this happening though, so far, it's all been fine).
Edit: I have now made lots of weapon-themed replacement lids for BIC biro pens. They are free to download on Printables here.
(I have a low-priced Patreon for anyone wishing to print my models commercially.)
The author marked this model as their own original creation.