Observant

Adjective

1. Alert and paying close attention; watchful.

   "The observant police officer noticed that my tax disk was out-of-date."

2. Diligently attentive in observing a law, custom, duty or principle; regardful; mindful.

   "I was normally observant of the local parking restrictions."

3. Practicing a religion.

   "She is an observant Catholic who goes to church regularly."