I'm thinking of storing my mnemonic seed on a few pieces of paper in secure locations, but I'm worried other people might find one of them and steal my funds. What are assume ways I can disguise this mnemonic seed so that people don't realize what it is if they find it?
You can do various things. Only the words' prefix matters (3 letter prefix for English, 4 letter prefix for all other languages I think), so you can modify the words (ie, if your seed has "marble", you might choose to replace it with "marked", for example). Now, you have what's essentially a stream of bits, and any general way of "hiding" these apply.
You could encrypt it (eg, GPG with your own key).
You could apply some "well known" transformation, such as writing it down backwards, etc.
You could apply steganography to store it into a picture of a cat.
You could do all these things at once.
But the thing to remember is that the more you process your seed, the more likely it is that you will misremember one of the steps. Could be you'll lose your GPG key, forget your password, delete the cat picture, forget it was the 4th word you swapped with the 8th, etc. So if you do any of this, the exact steps to "unhide" the seed are as important as the seed itself.
From fluffyponyza here:
Due to the nature of the key you can write it as part of something else - eg. write a fake love letter to your wife so that the 24 words on the left hand side are your key or whatever. Then write a bunch of extra love letters. That way, if your deposit box is ever discovered, it'll be disregarded as unimportant love letters".
Also, only the 3 or 4 first letters (3 for english, 4 for other languages) of each word matters
https://xmr.llcoins.net/ has some ways to add security measures to a mnemonic seed. This means even at attacker thinks they found your seed, they need to try and break the additional security.
Additionally, a mnemonic seed can be created from any 256 bit number, so any transformations you apply to a private key that don't change the bit length will have a seed. This allows a wide variety of cryptographic techniques to be used.
You could come up with your own mapping of mnemonic seed words, so that a seed word maps to a custom seed word that you've chosen. The mapping can be the first 25 words of your favorite book, a letter, etc. I'm not sure how valid this is, but even if someone got ahold of your seed, they wouldn't be able to restore your wallet. All this does is essentially require that someone find both the seed and mappings at the same time which is unlikely.
Using Shamir's Secret Sharing Scheme (SSSS) is probably a good alternative, if you want to hide the keys.
Nearly all Linux distributions have the SSSS package, on Ubuntu,
sudo apt-get install ssss
You can do an m of n split, and include thresholds in case you are worried about losing 1 of the keys for extra redundancy.
It would also be good for situations like wills too.
You could use a substitution cipher such as Rot13 or any of the others (Rot7, Rot8, etc). That's a simple way of disguising it.