Which of the following is a general indicator of meth labs?

The presence of containers with layers of both liquids and solids is a notable indicator of methamphetamine production. In the manufacturing process of meth, various chemicals are used, often leading to a distinct separation of compounds within containers. This layering happens because the different substances have different densities and may not fully mix, resulting in visible stratification. Observing such containers can raise suspicion and signal to law enforcement personnel that illegal activities, such as meth production, may be occurring nearby.

While other options could also raise concerns, they may not be as directly indicative of meth lab activity when considered in isolation. For instance, large cooking appliances might be present in legitimate cooking environments, and open flames could occur in various settings. Unusual plants might suggest other illegal activities like drug cultivation, but they do not specifically point towards methamphetamine manufacturing. The unique characteristic of layered liquids and solids serves as a strong sign of the chemical processes involved in meth production.