I spell my name with an apostrophe rather than a vowel for three basic reasons:
There are no true vowels in Hebrew, and I wish to have my name retain its Hebrew nature even when spelled with Latin characters. It is said in Midrashic (Jewish homolytical writings dating to hundreds of years before the Common Era) that the Jews merited liberation from exile in Ancient Egypt for three reasons, among which was that their names remained as Hebrew names.
I find that many computerinput systems still have difficulty handling names that use more than the typical 26 English characters; as a senior programmer for a major international firm, I find that testing a system by entering my own name is often enough to reveal hidden bugs, or programming errors, so that they can be fixed rapidly.
There are very, very few people whose name is D'n (or in female form, D'niella). I like being unique, and being remembered.