"WD" = War Department, for the British Army.Any reason why you think that?
ISD = "India Stores Depot", for the British Indian Army on India's budget.
EIC = East India Company property. However, EIC swords are not always marked as such, so lacking any marks doesn't mean that it isn't one.
Officers were required to purchase their own equipment, so as private purchases their swords wouldn't be marked as government property. That means that if the sword in question is marked WD, then it is probably a British Army sword issued to a cavalry trooper, or someone like that. A sword expert can look at a sword and tell if it's an officer's sword or a trooper's sword just by how it is made and finished (there are generally subtle differences, or in some cases they were completely different patterns). Officers' swords may also be completely non-standard, as it was their own property and they were only required to comply with standards up to a certain point.
Where this gets more complicated is that it was found in a police museum. It it was WD marked, then it was British government property. I don't know how this affected swords which were issued (as opposed to private purchases) to police, or if they had a different marking system, or what happened if they were issued swords which came out of army stores. Check to see if the swords themselves are marked, not just the scabbards. I'm assuming they go together just because you've shown them together, but I don't know that.
Of course the swords may have nothing to do with the police, they may have simply been confiscated from someone and kept around because someone thought they were too nice to throw out.