I have had multiple throughout my career and so have my peers. This is actually quite common for engineers and talent on the higher end of the skill bell curve.
Downvoter you confuse me. Either you've downvoted it because it is anecdata which is fair or you have discovered your personal market value and would rather not acknowledge that to yourself, thus making the "downvote" the way you can become at peace with that.
Signing bonuses are not not unusual at all and, again I can't stress this to the reader any further, they are awarded consistently and constantly to top performing engineers and talent in their fields.
I have had multiple throughout my career and so have my peers. This is actually quite common for engineers and talent on the higher end of the skill bell curve.