The ID Card Test is a process I use when naming characters. Once I've named the character, taking into account name meanings and name trends, I then think about how plausible yet unique the name is. There's no Princess Virtue Eaglebrook as one of my protagonists, nor is there a John Williams.
Where does that sweet spot lie, in which a character is named uniquely enough to be discernable from other characters and real-world people, yet also plausible enough to be a real name?
Imagine an ID card like this one:*
Now imagine you're working at a service desk processing ID cards all day. You'll inevitably see thousands of names. Some will be more common than others. Occasionally, one will surprise you.
Lots of names are ones you've never seen before in their first name-last name combinations, yet you're not surprised to see them. This is the sweet spot. These are good character names.
A pop culture example is when Ren & Stimpy creator John Kricfalusi named the famously irritable chihuahua Ren Hoek. Kricfalusi had apparently seen the name on a mailbox and found it sufficiently interesting. He never met the real Ren Hoek, or anyone else named Ren Hoek. It's a believable name, though, having clearly been proven to exist.
In that spirit, here are some character names from my recent works:
Karen Rothwald (State of Sin)
Max Blackwell (State of Sin)
George Clark** (Where Men Gape at Dust)
Victoria Rowntree (The Love I Feel Is a Burst Inside)
Simon Goldsmith (The Love I Feel Is a Burst Inside)
I've never met anyone with any of these names. If someone reads one of my books and says "that's my name!", though, I won't be surprised. After all, I have the same name as the protagonist's father in Flowers for Algernon.
Naming characters can be difficult. Luckily, there are millions of options. Getting to a name just uncommon enough for the reader to associate it with the book can be challenging, but can be very effective once you have it.
*Not literally an Arkham Asylum ID card, probably more like a standard-issue health card or driver's license. You have to admit, someone coming up with an Arkham ID is pretty cool, though. I wonder if they're issued to Shoggoths...
**Admittedly, this one is a little on the common side.