So, about a week ago, I noticed the lockette signs on two of my doors and on my chest were blank. All my items were missing from the chest, including a few diamonds, lapiz lazuli, redstone, etc.
Is there a way that a mod or admin could check who's opened the chest recently? Or are there any guesses as to what may have happened?

its very bad glitch with lockette it wipes your signs clear and all the contents of your chests, its happen to alot of people nothing anybody can do.... its not griefing it's a bug

Oh, it's a bug? Darn. No chance of getting my stuff back, then. D:

Yeah New Lockette bug, can't do much about it. Sorry.

Its actually a vanilla minecraft bug, not much we can do about it. Sorry.

Myotical, we were investigating the report you made, when a couple other members also report the same issue. What we found was a bug in the 1.7 update that still has not been addressed by Mojang.

Here is a link to a bukkit bug track page talking about it, but its not a bukkit problem (bukkit is the mod API that lets plugins like lockette chest protection to work). The problem, as has been confirmed via the bukkit guys, is in the base "vanilla" 1.7x Minecraft code.

Read the following page:
http://leaky.bukkit.org/issues/1052

I suggest you find another spot to store your valuables in for the time being. The chunks that this happens in seems to be odd, and allow it to happen repeatedly.

Yeah, I had guessed it must be that specific area; I replaced the signs, and they got wiped again.
So i just moved out. xD
Thanks for your help, though. ^-^