More than that - if you look at a folder filled with materials(shaders) and material instances(materials) there is not way to distinguish those
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If you look reeaally closely you can see that Materials have a Lime Green bar at the bottom, and Material Instances have a darker green color. It’s only slightly different and kind of hard to see, but it is there.
Easiest way for me to avoid any confusion is to use a naming convention. All my materials start with “M_” Material Instances “MI_”, and Material Functions “MF_”. Same goes for Blueprints “BP_” Textures “T_” and every other type of asset. It makes looking for a type of file MUCH easier. I can search for only materials from a list of materials, instances and functions just by typing “m_” for example. 
EDIT: I use the Shader/Material to mean the same thing as well all the time, but to me an actual Shader is HLSL code, not a material. Just the way I look at it personally.