Try to sign a transaction with signrawtransaction, but instead of using the uncompressed key as third argument, use a compressed key.
A meaningful error message.
The error message returned will be "Operation not valid with the current stack size".
3bf06e9bac57b5b5a746677b75e297a7b154bdbd
The same error appears in other similar situations (for example, if one tries to send an unsigned raw transaction). There could be some basic checking of inputs based on the length of valid input arguments, so say if input is X instead of the expected Y or Z bytes, a "Maybe you screwed up" message could be displayed. I think this would require less effort compared to advanced checking and would help detect a lot of simple problems that happen in the CLI.
I think this was fixed by #11288, so can be closed (unless anyone says otherwise)