It supposed to reflect the number of changes (in lines) to each file listed.
Plus signs for additions, minuses for deletions.
EDIT:
the 564 gives the amount of changed lines, and the - / + gives you the proportion of deletions/additions.
When the amount of changes can fit a line you'll get '+' per addition, '-' per deletion;
Otherwise, this is an approximation, e.g.
CHANGES.txt | 47 +++++++++++++++++++++++++++++++++
make-release.py | 77 +++++++++++++++++++++++++++++++++++++++----------------
2 files changed, 102 insertions(+), 22 deletions(-)
On CHANGES.txt since you can see that there are no '-', and since 47 '+' are a lot you have a proportionate amount of them (i.e. 100%).
On make-release.py you'll see x39 '+' standing for 55 additions and x16 '-' standing for 22 deletions.
Exactly as their proportion, and just the amount to fit output screen.
Hope that helps.
