You've probably got an input defined to look at /var/log/ and index the contents of it.
Splunk is looking at this file and telling you that it will not index '/var/log/sa/sa25' because it is binary. By default splunk doesn't index binary data, because it isn't going to be useful to you when you try to view it inside of Splunk.
This isn't really an error message, its just a warning telling you how Splunk is dealing with a file that it thinks it should index. You can safely ignore the warning, or you can blacklist the files from the input which is telling Splunk to read the data.
http://www.splunk.com/base/Documentation/latest/Data/Whitelistorblacklistspecificincomingdata
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