message for job finishing runing background in Bash

Hi,
I call "set -o notify" to notify me when my background jobs finish. I find that the messages upon finishing are different: for some job, it starts sometimes with "[jobID]", sometimes with "[jobID]+" and sometimes "[jobID]-". I wonder what they mean actually? Do they mean the jobs are finished abnormally?
Thanks and regards!

Here's from the bash man page under JOB CONTROL

Quote:

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In output pertaining to jobs (e.g., the output of the jobs command), the current job is always flagged with a +, and the previous job with a -. A single % (with no accompanying job specification) also refers to the current job.

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