Maryland Code, Transportation § 21-103

(a)(1) A person may not willfully disobey any lawful order or direction of any police officer.

(2) This subsection may not be construed to authorize a police officer at a motor vehicle checkpoint, as defined in § 25-114 of this article, to target only motorcycles for inspection or evaluation, except as appropriate at a police checkpoint established as part of a police search or investigation.

(b)(1) A police officer may summon witnesses to testify under oath on any charge brought under the Maryland Vehicle Law.  1

(2) A person may not willfully disobey a summons.