Feminized and autoflowering cannabis seeds do not differ visually from the regular seeds. It’s the same with C. indica or C. sativa species and those which are grown specifically for industrial purposes, usually referred to as industrial hemp. It’s also worth knowing that marijuana seeds can be the size of millet groats, but there are also some which are as large as lentils, although generally they are the size of a grain of rice. Usually sativa seeds are bigger than indica. If you want to be sure of the authenticity of your seeds, you should buy them at reputable seed banks which provide high quality certified seeds.