To display numbers in a sub-grid / view you will need the number to be on the record (as a field). You can autonumber the records in CRM and then show that column in sub-grid. Google for Autonumbering in CRM and you will get ready to use tools as well as
the plugin based approach. JavaScript will not be ideal if you consider multi-server and heavy load systems. As far as I know, this solution would be same for either CRM 2011 or 2013.
If you are only looking at sequential numbering of records in the sub-grid then I'm afraid its not possible using supported methods. Instead you can get a Report that has serial numbers in the first row.
hope this helps!
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