Actually I am not sure if this can be deemed adab at all. Mourning or any semblance of mourning does not look like adab to me. Allah knows best. Even if it's adab, the fact that it comes from the shias and has the mark of shias written all over it, makes it, in my view, impermissible( of course, we should ask a mufti sahab about it). I would go further and argue that we should in fact encourage marriages in Muharram, not with the niyyah to dishonour or make fitnah, but with the intention of clarifying a fiqhi point and stopping our people from resembling the heretics. Just like some of our brothers have chosen to mention the fazaail of Hadrat Muwawiyah( radi Allahu anhu) even on the 10th of Muharram, to educate the masses and expose the hidden rafidis among sunnis.