Some artists, my boyfriend included, have a problem where:
They upload an image they drew of, let's say a trans woman for example. They tag the pic gynomorph. They explain in the art description below that the character is she/her.
Later on, a viewer comes along and tags the pictures male instead, because they see a penis.
The owner of the character (either the artist or commissioner) becomes upset that they were misgendered.
A back-and-forth follows, the artist changing it back, and viewer(s) changing that back.

My solution for this is that artists should be able to lock the gynomorph and andromorph tags so that they cannot be changed by others who frankly don't have a say in the gender of the character in the picture.
If they can already, please explain how one does this.
If they cannot yet, then consider this my explanation for why this needs to be a feature.
Considering that the alternative is that these artists are considering putting themselves on the DNP list to protect their clients from such misgendering, I think that my suggestion is a better option.

gynomorph_(lore)
andromorph_(lore)

Also trans_woman_(lore) and trans_man_(lore)

e621 as an archive runs on rules and policies, one of them named "Tag What You See", as you can see here.
In overall, only what is visible on the image is worth of tagging. If the character is visibly male, it'll be tagged as male, no matter what gender the character has.

However, in addition to what was already replied, e621 adopted the Lore tags, that allows character/art owners to identify character's genders. Those can be read about here and here.
Lore tags work independently (and will not replace) from the general tags. They're meant to display external info such as the character's gender.

OP might also be interested in the visibly_trans tag.

Perfect, thanks you guys, we'll give those tags a try. Peace!