I have created several small symbols which I must use frequently in a book length document. Is there an app to allow me to store these symbols and insert them as needed when typing in iBooks Author or Pages by using some short key combinations?

They are vector graphics made with Affinity Designer. They could be easily .jpg or .png if needed. Currently I use copy and paste which works fine (i.e. the vector graphic inserts well in the document) except for the tedium of copying and pasting.

Thank you for the suggestion. I have found copy and paste to be adequate. Since I use certain symbols so often in this work, I can copy and paste from the nearby parts of the document without too much trouble.