Personally, I like a serial # on a knife. I only have a couple that have it. But there are pros and cons to it.
The negative side is the added time and expense to serialize a blade. Whether it is stamped, engraved, laser, etched, it adds to the workload, not to mention keeping records of the numbers in some sort of a file or database.
The benefits of it are numerous.
1. You are perceived as better and higher end with your customers.
2. You have a definite way to record what you make and when. If you start having customers complaining about a bad heat treat, your records would show when it was made, and then you can trace back, hopefully being able to determine what batch of knives got treated by so and so, and address that issue if needed. From a product liability standpoint, I would want to know and correct a batch of bad blades out there with my name on it.
3. If you become famous for your knives, a not uncommon dream of many, you add value and also provide protection for yourself and your customers down the road. Some guy calls up and says, "Hey I am looking to buy one of your old "Skeeter Skinners" you used to make. It has serial number 1940. Can you tell me anything about it? What steel did you use?" A quick check of your records can show, "I never made a "Skeeter Skinner" with that serial number. The only ones I made had numbers 0067 to 0548. The knife you are looking at is a fake. Not my work"
4. Added value to the customer. From my rock & roll days, there is a microphone manufacturer who is famous for wanting to know if any of their mics ever get lost or stolen. You lose a mic, let the company know. If it ever crosses their hands for service, or an inquiry, they grab it and make sure it gets back to the rightful owner. Blade makers can do the same thing; Even if only comes to knives coming in for re-sharpening.
5. As one who used to have a great memory I can definitely say it ain't perfect, and it may not last even if it is now. It is easy to recognize your work a year or two after the fact and recall the details. 20 years, definitely not so easy. One's own craftsmanship changes of time, improving hopefully. Not always easy to spot your own handiwork later on. I know wiring work I have done in the past can look completely foreign to me at times.