There's an item after Merchant Scene 5 (Missionary) which gives a lewd crest tattoo on MC belly for 'Main Menu Stand' figure, but the added item have unspecified description:
I haven't checked this in item data yet since there's a need to look for item id in separately located files, but for now I'll assume it's a placeholder with no practical effect.
Oh yeah, here's a sprite sheet with all items, including some unused/debug ones:
Update: Okay, so I pulled this Merchant Crest item data and currently it only gives you 10 Evil Points for now:
[72]
0 Item data
0 int id = 72
0 int name_id = 974
0 int icon = 72
0 int desc = 975
0 int type = 0
1 string show_place = "-1"
1 string tags = ""
0 int add_level = 1
1 string pre_item = "0"
0 int atk_add = 0
0 float hp_add = 0
0 float mp_add = 0
0 float hp_recover = 0
0 int buff_add = 0
0 int buff_remove = 0
0 float move_add = 0
0 int luky_add = 0
0 int maternal_add = 0
0 int evil_add = 10
0 int holy_add = 0
0 int add_state_hurt = 0
0 int add_state_attack = 0
PS:
0 int add_level = "1" is a curious part because only items related to post-run unlocks have it, like Holy Cross after post-virgin run)
1 string show_place = "-1" - I don't get this one. Maybe it separates this item from the rest - can't be unlocked in a post-run screen, can't be picked up in shop or areas... code is undocumented so I'm just guessing for this part.
So yeah, nothing special for it for the time being.