It's important to know your bike's serial number.
Probably the most common question we get here at Bacchetta is a two-part one: (a) where do I find my serial number, and (b) can I use the serial number to determine the age of my bike? Below are pictures of a variety of frames, showing where the serial number is located. I hope this is helpful:
All aluminum and steel-framed bikes (except the first batch of Corsa frames and early steel Strada frames) - the serial number is located on the head tube of the bike, on the back side, just above the fork (shown above). The serial number is a clear sticker with black letters/numbers on it. You will also see a number stamped into the frame under the sticker. While this number does not correspond to the sticker, you may be able to tell the size of your bike by whether it has an S, M or L at the end of the top line.
The CA2.0 has a sticker across the rear brake bridge. This picture does not show the sticker (I didn't have a CA2.0 frameset to photograph), but shows exactly where the sticker would be located. A little known secret is that there is a serial number sticker inside of the bottom bracket. If you remove the cranks and bottom bracket, it is easily visible in there.
If you have a Ti Aero or first-generation Corsa (made in the US), the serial number is stamped on the bottom bracket shell at the front of the bike.
Shown above, you can see the CA3.0 has a tiny sticker under bottom bracket. Personally, I cannot read it without good glasses. The serial number is the upper number.
The original Carbon Aero has a serial number location similar to the Ti Aero. It is stamped on the front side of the frame just below the bottom bracket shell.
Early steel Strada frames also had the serial number located on the front side of the bottom bracket shell.
While Bacchetta is no longer involved with the Carbon Trike, if you are looking for the serial number, it is located on the inside of the opening in the frame.
As to the second part of this question, there is no way to tell the age of your bike based on the serial number. The old owners of Bacchetta did not have any historical data to send us. If you have purchased a new new bike since about July of 2021, we probably have a record of the number. As we start getting new batches of frames in, we will update this article.