An ECDSA signature for example can be represented as 64 bytes with good security, and adding 64 bytes to a PDF417 isn't too big of a deal. That's basically just

An ECDSA signature for example can be represented as 64 bytes with good security, and adding 64 bytes to a PDF417 isn't too big of a deal. That's basically just the curve coordinates and nothing else though, so the verifying device has to either guess-and-check or use some other data to figure out what public key it should be verifying against, and there's no expiry or anything like that. In practice, now that we have elliptic curve algorithms that tend to allow very compact keys at a good security level, the bigger problem is less the actual cryptographic signature and more all the PKI metadata that normally needs to be tied to a signature to make it useful (especially if you have multiple levels of authority, which you probably want to or revocation becomes a huge problem). There are ways around carrying around PKI metadata with the signature (i.e. a normal x509 certificate) but there are tradeoffs and it's not like a well-established standard, which tends to make government organizations uncomfortable about adoption.