Today, my client has been quitting unexpectedly while I create and edit signs in single-player. I'll be lucky if I even finish a sign because the client quits randomly while I edit the sign. Crashes also occur even without placing signs, but they are much, much more likely to occur when creating signs.

Minecraft quits for the reason "Minecraft has quit unexpectedly. Click Reopen to open the application again. Click Report to see more detailed information and send a report to Apple." No crash log is produced/saved upon crashing.