https://bloodborne.fandom.com/wiki/Notes
That said, some people get creative trying to bend the system into new uses, for example "amazing chest ahead" in front of an NPC rather than a storage location. Or "try tongue, but hole".
The message system also gave rise to a tradition of calling people "skeleton" when encouraging them on Reddit and elsewhere. In Dark Souls 2, a bunch of skeletons were placed in the world by the designers, and players started attaching creative messages to them:
https://66.media.tumblr.com/27bb20783b49cf5e63522c3f51092e4a...
https://i.imgur.com/0ewexGV.jpg
https://i.imgur.com/ZpENzv8.jpg
https://66.media.tumblr.com/01d2e6acf80247332b937db84c45d2fc...
An interesting feature is that you can rate messages, and if your message is rated (good or bad) you get back full health. There are many threads from players that managed to beat a boss because of this, but you can't abuse it because you can't reliable expect it to happen at the right time.
Not all messages from players can be trusted. There are many "illusory wall ahead" messages in front of places that look like they should have a secret door, but don't. Then you'll spend some time hacking at a regular wall. There are also messages that say "try jumping" in front of cliffs where you die if you jump off. This creates an extra level of connection to the players who left the message, because you have to consider if you trust a random person you never met or not, and if they trick you, you get that human element in a situation that was supposed to just be a regular cliff. Someone spent time setting up that joke for you. Sometimes jumping does work, and you hit a hidden platform and find some loot, so you never know.