Hi-

There is this column in the 3dClusterize tabular output:

Max Int      : Maximum Intensity value for the volume cluster

... so the sign of that should tell you which cluster is pos/neg when using bi-sided (generally recommended) clustering.

In the GUI, when you hit the "Save Mask" button in the Clusterize Report controller, you will see the 3dClusterize command run on the commandline for you, as well; you can redirect that table to the file.

Just in case you are bored and want some related reading on the topic of using stats/betas for different aspects of reporting, then you could take a look at:

1) Is the statistic value all we should care about in neuroimaging?
[www.ncbi.nlm.nih.gov]
(Hint about the title: the answer is "no".) This describes why using more than stats is important, and the separate roles of the stats and betas in interpreting your results.

and

2) A tail of two sides: Artificially doubled false positive rates in neuroimaging due to the sidedness choice with t-tests.
[www.ncbi.nlm.nih.gov]
which is covers (among other useful bits) how bi-sided or two-sided testing can still allow you to tell which clusters are positive and negative.

and here might be a useful example of automatically taking snapshots of your stats results:
[afni.nimh.nih.gov]

--pt