This information is public in Khorvare, but probably only those who deal with the houses outside of public transactions find it interesting enough to remember.
House Script
House Script is a secret Language spoken an written by members of each House. The Houses each have their own individual version of this script designed to keep its IP secret from the uninitiated. Knowing one house’s script does not allow you to decipher the any other House Script
Key response
House script is also often used as an informal method to checking that someone claiming to be a member of a house is indeed one. Agreements between houses gives certain call and response passwords with House scripts which act as a confirmation of identity between House agents.
Lyrandar Pilot: “Nazdar shok” Cannith Maker: “Darim” Lyrandar Pilot: “Good to meet you friend, let us commence negotiations!”
Gaining House Script
Any character with an intelligence above 10 who is or was a member of a House gains the additional language “House Script (House Name)“.
House Cypher
Higher level top secret documents and IP might use the further security of the House Cypher. This uses a magic Item Enciphering band (wondrous item, common, cursed) and a spell Deciphering Dweomer to encrypt and decrypt the House Script.
“Getting the band” is often used as a phrase for rising within the house and gaining trust.
Enciphering band (wondrous item, common, cursed)
This plain looking golden strap fits around the writing hand of a scribe like the strap of a timepiece (and indeed such straps are sometimes enchanted similarly). When the wearer attempts to write in a language they know, the bracelet will interrupt the subconscious reflexes of the user (Strength save DC 5 to resist) and cause them to write in a cypher predetermined by the bracelet’s creator. Once attached the band cannot be removed except via a remove curse spell to make it harder for the bands to be stolen.
Deciphering Dweomer
2nd-level spell, illusion Casting time: 1 hour Target: a Dragonmarked creature Duration: until dispelled When cast on a Dragonmarked individual, the caster chooses a house script the caster and target both know and imbues it into the spell. The spell’s magic is then sustained by the Dragonmark of the recipient. As long as the spell remains active, when the target attempts to read cyphertext encrypted in the chosen script, the spell will cause them to see the decrypted plaintext of the message instead (the reader is aware when this is happening).
Any house member in good standing likely has the decrypting dweomer cast upon them to read house script, but if the effect is dispelled reading such texts is much more difficult, as they would then need to manually decrypt any written text, a much slower process. And the houses tightly control who gets to cast decrypting dweomer, it’s not a spell you can choose at level up and they avoid writing scrolls for it, so if you need your dweomer refreshed for some reason you need to report into your house to have it recast.