How do I view or verify signed .mobileconfig files using Terminal?
Apple's .mobileconfig files are signed using PKCS7. The signing certificate data can be shown using the following command:

openssl pkcs7 -inform DER -print_certs -in ~/Settings.mobileconfig


You can copy/paste ASCII certificate data from the output into a plain text file (with a .cer filename extension) to create copies of the certificates:

-----BEGIN CERTIFICATE-----
MIIElTCCA32gAwIBAgIBAjALBgkqhkiG9w0BAQswga4xQDA+BgNVBAMMN0tlbGxl
eSBDb21wdXRpbmcgT3BlbiBEaXJlY3RvcnkgQ2VydGlmaWNhdGlvbiBBdXRob3Jp
dHkxGTAXBgNVBAoMEEtlbGxleSBDb21wdXRpbmcxJTAjBgNVBAsMHE1BQ09TWCBP
...
q19fbG33zNwRhVHceYMpcbWG1MSqLxnPu4wo75OZFIJCaByZykfpKAzRZl9aa7rD
5bAuzZAziXBW7WWKce2a4hGN804W9RHco5HIGLsQAdg4pLZvENXF1+JNHtBVXjjL
WJrCDKjnCyS1DqmJqijk9KIDM8gP6iLLeQ==
-----END CERTIFICATE-----


OpenSSL can be used to verify the code-signing certificate as well. Assuming that we've copied the signing CA's certificate text/data into ~/CA.crt, and copied the code signing certificate into ~/CodeSigner.crt.:

openssl verify -CAfile ~/CA.crt ~/CodeSigner.crt


Removing the signature from a file can be accomplished using this command:

openssl smime -inform DER -verify -in ~/Settings.mobileconfig -noverify -out ~/Unsigned.mobileconfig