What does this sticker show?
 

As a brand new owner of a not-so-new '01 X5, I've been looking it over, and trying to match items on the truck to corresponding info in the online owner's and workshop manuals that I've downloaded. I saw this circular sticker attached to the driver's side door frame, but can't find any reference to it in either source. What # is ticked-off (321 or 341?), and what does it mean?

A recall campaign or SIB work was completed. You will have to lookup exactly which one though.

recall or SIB lookup?
 

I checked the NHTSA.gov site and entered my VIN...found no "current" or "not performed" recalls on it. Then I tried looking for SIB's, by googling "BMW SIB 321", and "BMW SIB 341" (assuming that either 321 or 341 is the covered-up number), and each time, a single SIB (for another model) DID show up, but none for the E53.

I can't find any direct list of SIB's that may have been done by the original owner (he had it 'til 2018). I'm the third, after my neighbor bought and restored it for me (as a swap for my drag car).

Is there another way to trace this, or do I need to purchase a VIN tracing report (Carfax or Vin-decoders, among others)?

The missing number would be 321 but I can't say I've ever seen a sticker exactly like that before... :dunno:

You could go to a dealer and ask them. Tell them you just acquired the x5 and are wondering about open recalls or other campaigns and saw that disc. If they aren't complete tools, they should tell you what it's means.

no open recalls, not urgent to learn the answer
 

I try to avoid dealerships if I can; over the last fifty years of interacting with "them" (i.e.: Chevy, VW, Dodge, Volvo, Ford, Nissan, Pontiac-GMC, Hummer dealerships), I've had favorable impressions with only 4 out of say, 20 I've visited. Whether making new or used car/truck purchases, getting required warranty service or just buying parts, only three Chevy and one VW dealerships fully treated me well, everytime.

So, I'm in no hurry to meet the BMW dealer quite yet. I'll soon need to get a second key, though, and might have to resort to going to the dealer for it, but since no open recall is shown on the BMWNA or NHTSA websites, it'll wait.

Understand that. I too avoid stealerships if possible. For your key try bimmertech if you don't mind submitting ownership docs on their website. Much faster and cheaper than a dealer in most cases. Just got a new key for our f15 x5. With the blade key was about $500. Dealership wanted something like $800 with "programming," which was of course just holding the key to the column and initializing it with the vehicle.

e53 keys not covered by bimmertech
 

Looks like bimmertech doesn't have keys for my '01. Out of luck, again.

Yeah, didn't notice they did not cover the older chassis with the diamond style key. Sorry about that.

Try https://www.thebmwminipartstore.com/replacement-keys $170 but you will need to provide proof of ownership.