I've seen various methods used:
- Checking in to Plugshare
- Putting name/phone number in a note on the dash
- A hanging tag around the charging cable
The benefit of Need2Charge is that you only need to do it once, and that's it.
When you sign up it provides you with a custom PDF which includes a badge with a QR code specific to your account. You can put this badge on you car windscreen. Whenever you are parked at a charger, people can either scan the code on their phone, or type in your registration plate on either the Need2Charge app or website, and they can notify you that they are in line for the charger. You get an alert on your app and can have a two way message.
Personally I think as EVs become more mainstream, I think this sort of system will scale better than Plugshare.
Here's a pic of my tag, cut out, laminated, and stuck to my windscreen:


I just leave it there all the time no matter where I am.
The same PDF also has some notes that you can cut out and leave under people's wipers, in case the person isn't using Need2Charge. This is handy for spreading the word about the existence of this app.

Common questions:
Don't you have to enter the country/state as well as the plate number? Just the plate number. If two people in different jurisdictions with the same plate try to use the app, there may be problems! Very unlikely for the time being. The developer is aware and said it can be fixed if it becomes an issue, but the risk of conflict is very low!
Does it cost anything? No, it's free to use. There are no ads either. In the "About" section of the app, the developer has some referral links that he invites people to use in order to support the app. Note that one is a Tesla referral and the others are for UK companies, so not particularly easy for us to support, but hopefully it does the job.
Should I stop checking in to Plugshare? Not if you don't want to! I still do, so I can be contacted via either method. Checking recent check-ins is a still a good way to see if a site is generally reliable and available, or frequently has issues.
Does it work if I have more than one car? Yes, you can link more than one car to your account.
Doesn't this only work if everyone is signed up? Yes, but other systems like Plugshare have that problem too, and for that to work people need to check-in every single time. But if some people start to use Need2Charge, including displaying their tag and putting notes under windscreens, others will see them, and in turn it will encourage some of them to sign up as well. You can still communicate with a registered user even if they don't have a tag visible on their dash by entering their rego plate.
So I'm interested to hear peoples thoughts on this one. I'm happy to write it up as an AEVA website article if people think it's a good idea?