Years ago, when Pioneer DJ introduced the DMP-555, one of the first true multimedia source players for DJs, they used a closed ecosystem that required users to prepare their digital media (MP3s) for the player through the DJ Booth software and export to an SD card (this was before USB drives were a big thing). It was designed with the integrity of copyright protection in mind, and it was Pioneer DJ's attempt at showing the music industry, which was reeling from the advent of file sharing / Napster, that DJs were not going to be part of the problem.
The intention was that the files were encoded on the SD card and could only be read by the DMP-555 and the software used to put them there. If you deleted the encoded file directly from the SD card, you could only copy that file out from the software to an SD card a maximum of 3 times. After that you could re-import the file again and repeat it (silly, I know). The other option was you "unloaded" the song from the SD card, freeing up one of the transfers. And no, you couldn't stick that SD card into someone else's computer or DJ Booth software and read it - it was encoded to ONLY the software installation on which it originated.
Unfortunately what happened was someone found out that you could use a (then) cheaper and more readily available MMC card and simply copy an MP3 to it from your computer ... and it would play in the DMP-555!
The other unfortunate failure of the DMP-555 was that it came out before the industry was ready for it. It was almost double the price of the other CDJs available, and while it had some nifty tricks up its sleeve, wrestling with difficult software and low capacity MMC/SD storage options was not something DJs wanted, so the player faded to the background.
With huge USB / SD storage options available at pennies per GB, it's a breeze to store your entire collection and precious original works on a portable device that can easily be left behind, but if the track record for "securing" media is anything to learn from, I don't think Pioneer DJ will go down that road again. Even if there were some kind of password protection built-in, that would likely mean the drive and its contents would have to be encrypted, which means more work for the system to encrypt on export, and decrypt on playback. That's only going to slow down the process and make it more expensive for the hardware and the software to implement it.
So it really is up to you, the DJ, to keep track of your devices and make sure they're not left behind for others to obtain!