Hello and welcome!
My space marines are from a friends custom chapter, dating from the rogue trader days
The Deaths Head recruit from an imperial medieval world, so heraldry and knights of old theme -I use the fantasy empire horse heads to decorate my vehicles, empire knight shields as combat shields etc
My company markings don't duplicate the markings my friend uses, so if they should ever be fielded together there is nothing duplicated - eg no two captains of the 5th company, no duplicate first company squads etc.
A few pictures that are here in my gallery -