Medtech Europe have created a guidance document that discuss use of certain symbols like the Medical device symbol - MD-, devices that includes Different types of substances and translations etc. the documents can be found here. These guidance are useful since you wiull know that many comnpanies will use it and hence the power behind this will be strong vs that you find symbols yourself. They have of coarse not just created them, but refers to different ISO standards.
General speakiong, using already existing standards are always better than create something yourself!