what does tracking number begining with RS mean

Mike, the last two letters of your tracking number really matters. It can reveal where your parcel is sent from. Those tracking numbers starting with R refers that is Small Package Service.

Asking about prefix, not suffix. The Wikipedia article says RS is "Letter post: registered, but not insured delivery". I think that also covers small parcels; I'm waiting for a cell phone mailed with an RS prefix.

The suffix in my case is GB, but the item was mailed in China. My understanding is that where multiple service providers exist within a country, the suffix will identify the provider, not the country.

I don't think these items are actually trackable, though. Maybe by the service provider, but I have had items mailed this way before that never show up in anyone's tracking system.

It's very poorly documented, and it would be really, really nice if someone could take the time to provide a comprehensive overview of the system and the implications of each prefix. Any volunteers?