Crown & Anchor dice. They have a crown, anchor, heart, diamond, spade and club on the facets, with crown/heart/diamond as red and anchor/spade/club as black. And like most roleplayers who find funky new dice that they like, I'm searching for a way to use these things that would make sense in a game.
What they reminded me of was the passage in the first edition AD&D Dungeon Master's Guide where Gygax describes the dice he had with hearts, clubs, spades and diamonds on the different faces, and using them as reaction dice. I'm thinking that crown & anchor dice are even better for these purposes since they allow more spaces for interpretation. In the following, if you don't have crown & anchor dice, you can use a standard d6 with an odd/even interpretation of 1 - Crown, 2 - Anchor, 3 - Heart, 4 - Spade, 5 - Diamond, 6 - Club.
The red suits are positive reactions, just as Gygax had it, and the black suits give us the negative reactions. But the specific suit rolled gives us the quality of the reaction, the type of response that the NPC or monster encountered has.
Crown (1): For intelligent encounters, this should imply a rational reaction. An NPC or monster should be open to negotiation, relative to the situation, or able to be talked out of any kind of rash action. With unintelligent creatures, animals and such, this should mean that the object of the encounter is deferent to the characters.
Anchor (2): This indicates a territorial stubbornness. It may be of the "you shall not pass!" variety, or the growling and hissing of a wild beast, without implying outright attack. For whatever reason, the subject is simply in a bad and irrational mood and not prone to any cooperation.
Heart (3): The heart indicates that there is some immediate compatibility between the characters and the subject of the encounter. Even an otherwise implacably hostile creature will hesitate to the attack on a roll of heart, and with unintelligent animals it is possible that they will actually follow the character(s) around like a stray dog. (Not that this is always desirable.)
Spade (4): While not an "immediate attack" roll, this one means that they don't like you. The opposite of the heart, a spade roll just isn't going to warm the cockles. The character is immediately disliked and eyed with suspicion. Animals and such will growl and nip, or just run away.
Diamond (5): Keeping with the theme of what diamonds represent, this indicates that the subject is willing to be "bought off" in some way, shape or form. This may be a monetary bribe, a favor, or simply giving a bit of food to a wild creature. Town guards and such may automatically be considered to roll a diamond.
Clubs (6): And now we get to the old violence. A roll of clubs means that the subject of the encounter is immediately hostile to the point of physical attack. It pretty much had to happen on some facet, and the clubs just seem the most direct way to do it.
If you want to give a character with a high Charisma a better shot, consider re-rolling Clubs; likewise for low Charisma, re-roll Crowns because their luck is bad. The second roll should then count even if it's the same as the first.