From this SO question:
U: Working file was updated
G: Changes on the repo were automatically merged into the working copy
M: Working copy is modified
C: This file conflicts with the version in the repo
?: This file is not under version control
!: This file is under version control but is missing or incomplete
A: This file will be added to version control (after commit)
A+: This file will be moved (after commit)
D: This file will be deleted (after commit)
S: This signifies that the file or directory has been switched from the path of the rest of the working copy (using svn switch) to a branch
I: Ignored
X: External definition
~: Type changed
R: Item has been replaced in your working copy. This means the file was scheduled for deletion, and then a new file with the same name was scheduled for addition in its place.
L : Item is locked
E: Item existed, as it would have been created, by an svn update.
Note that these are SVN status codes and some of them do NOT apply to XCode as @Zaph pointed in comments. Anyway I think most used are included in this link and are valid in xCode too.
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