If you have a non-life threatening matter you would like to report to the Houston Police Department, please dial (713) 884-3131. Save this number on your cell phone. DO NOT use 911 unless it is a life-threatening emergency.
Anyone encountering suspicious activity should report it immediately to HPD. Do not brush it off or hope someone else reports it. If it looks or sounds out of place, report it.
Source: Houston Police Department Contact Page, https://www.houstontx.gov/police/contact/