Every bicycle that I've owned or serviced has the serial number stamped into the lower side of the bottom bracket (BB) housing. However the some instruction manuals I’ve reviewed indicate that the rear dropouts may have the serial number stamped on the inside of it. The front fork (if a shock fork) may also have it's own serial number.
An important issue with Aluminum Frames is their design life. Unlike steel and titanium, Aluminum will only take a finite number of stress cycles. While the manufacturing engineers design "extra" strength into Aluminum Frames to accommodate this, it least one major US bicycle builder is on record for stating a five-year design life for their Aluminum Frames.
Ask the mechanics at your Local Bike Shop (LBS) about Aluminum and frame failures and there is a high likelihood you will be told to "check the welded areas carefully for any signs of cracks” Although without "calibrated eyeballs" you might miss these sure signs of structural concerns. As for paint, Aluminum is sometimes "clear coated" with a polymer that makes it appear "unpainted".
If you are intent on extreme sports use, then please do have a skilled veteran mechanic look the frame over before you attempt any maneuvers that would challenge the integrity of the machine. Today I’m replacing a font fork (Shock absorbing variety) that sheared off at the steerer tube weld during a high impact-loading maneuver. In speaking with several LBS mechanics they indicated that the evolution of the shock absorbing front fork has now moved completely away from welds on the steerer tube, they are all now force fitted into the fork crown.
Extremely important resources are the “Recalls” listed on the Consumer Safety Commission’s Web Site http://www.consumeraffairs.com/recal...alls_sport.htm
Products are listed by year and vendor, also you can use it’s search engine with the serial number and find if there known significant issues with your product. There are many different bicycle vendors and models comprising thousands and thousands of individual bicycles currently on recall! The Front Fork unit that I’m replacing was on recall, which affected “24,800 mountain bikes” and was shipped to me at no charge by the vendor. Side Note: I had to request the replacement, it was not volunteered without solicitation.
Sadly the LBS community doesn’t endeavor to contact the folks to whom they sold the faulty equipment (it is the bicycle Vendor’s responsibility I was informed), however they do post the “Recalls” on their service departments bulletin boards, which is good.
And please always wear a helmet, ride within your known abilities especially in remote terrain and never ride at night. Thank you…