How to tell the difference between METAR and SPECI reports?
I don't think you can use METARs to produce precise hourly rainfall data. METARs do not express the exact amount of precipitation; rain is only expressed in three categories (light, moderate, heavy).

The way I understand your problem, you want to skip SPECI reports because you only want a single report per hour. A better way of doing this would be to use the time/date stamp in the report and simply dismiss a report if you already have one from the same hour. Say you have a report from 011203Z and you then receive another report from 011220Z. You want to dismiss the last report, because it is only 17 minutes older than the first one.

Alternatively, you can find METARs from a number of other sources, which include the message designator as well. Here is one I find useful: http://www.ogimet.com/metars.phtml.en