I received a very nice e-mail from Christina (I tried to reply but her e-mail address probably contains a typo) who had a very interesting suggestion.
As a result, something is happening on Zazzle.com: Hilda the Wicked Witch proudly presents her own T-shirt line:
If you are, by chance, interested in acquiring such a shirt (or hoodie, or raglan shirt or…), you can follow this link to make it to the store!
For people not into t-shirts, there is also Hilda’s official coffee (or tea) mug:
You can find the mug here. (As the store is still entirely new, the products do not show up in searches etc. This is beyond my control.)
(Thank you, Christina, for the idea!)