I personally think the tagging system should be sufficient. Any NSFW sheet (and only NSFW sheets) should be tagged NSFW anyway, so a separate way of specifying it isn't necessary.
The "age verification" thing where you input a date of birth is possible, then again they don't really do much beyond requiring people to make a few extra clicks. A button needing to be clicked is just simpler and isn't any less secure. I do think that a checkbox should be available along with the button though, something like "don't show this warning again" or whatever. If checked a cookie can be stored, but if left unchecked then it shows up every time (even if people click the button), for those who are using a shared computer or just want to view that specific sheet but avoid NSFW in general.
I think there should also be an option for registered users, so that you can, for example, have the warning disabled while logged in but have it active when not.
In any case, I think such a filter is a good idea. I also agree that it should only apply to sheets, however games should also be able to be tagged NSFW (if most or all of its sheets are NSFW).
The "age verification" thing where you input a date of birth is possible, then again they don't really do much beyond requiring people to make a few extra clicks. A button needing to be clicked is just simpler and isn't any less secure. I do think that a checkbox should be available along with the button though, something like "don't show this warning again" or whatever. If checked a cookie can be stored, but if left unchecked then it shows up every time (even if people click the button), for those who are using a shared computer or just want to view that specific sheet but avoid NSFW in general.
I think there should also be an option for registered users, so that you can, for example, have the warning disabled while logged in but have it active when not.
In any case, I think such a filter is a good idea. I also agree that it should only apply to sheets, however games should also be able to be tagged NSFW (if most or all of its sheets are NSFW).