Look for the author(s). What academic degrees do they have? Where do they work? Are their degrees and work experience related to the topic of the article? Could they be considered to be experts in the subject?
Scholarly sources are written by researchers with academic degrees (that is, advanced university degrees) and/or experience working in the subject.
Look for the content and purpose. What is the article trying to achieve? For example, is it trying to entertain, to inform, to sell a product, to report on research, to convince, to argue, etc.? What is the intended audience of the article--the general public or experts in the topic?
Scholarly sources are written by researchers about research they have conducted, in order to share their findings with other researchers.
Larger Publication/Review Process
Look for the title of the larger publication in which the article appeared. What kind of publication is it? Who is the publisher--a publishing company, a university, a professional organization? Does this publication have a peer review process?
Scholarly sources are generally published by reputable publishing companies (like Wiley), university presses (like the MIT Press), and professional organizations (like IEEE, the Institute of Electrical and Electronics Engineers).
Scholarly sources go through a pre-publication editing process called peer review in which people who are peers to the author (researchers and experts in the same field) evaluate the source to ensure the research is valid.
Look for a bibliography or works cited list. Does the article cite other sources in a formal way?
Scholarly sources always include a formal bibliography or works cited list.
Look for images. Are they mostly artistic and decorative--for example, a photograph of the research lab? Or do they provide informational content necessary to understanding the article--for example, a chart that provides data from an experiment?
Scholarly sources generally have few images. If images are present, they are usually things like charts, graphs, tables, diagrams, etc., that provide information necessary to understanding the article.
Note: The answers to some of these questions may not be in the article itself. You may need to do some searching online to find the answers.