All states will provide you with written documentation of the Handicapped Placard status at the very least, for travel.
If you find yourself at your destination in Florida without that documentation, you will be ticketed if you park in a Handicapped spot without displaying such documentation. Florida DMV advises to either have a Temporary FL Placard issued, or dispute the fine with written documentation sent to them after you get home, in which case the fine will be reduced, but there is still a fine even for anyone with Handicapped status parking in designated spots without displaying their Handicap documentation.
Best to try and plan ahead.
I'm sure all states have a plan and realize that there are rules about documentation. My main point was that all states do not use the placard or at least have other alternatives. Some use stickers, some use tags as well. It's also common to see them laying on the dash rather than attached. The bottom line is that unless you go look at a given car to see if it's properly documented, it may be and a look at the rear view mirror may not reveal that. Also, while it may not be legal to park if you don't have the proper documentation, some may not know that and still be HC such that they need the HC parking. I have no patience or sympathy for someone who parks in a HC spot inappropriately and I've been chastised here in the past for even suggesting that some may take advantage of these options at times but some do. It's also easy to get a placard without actually needing it.
When the states agreed to honor the handicapped parking permits of each other, they agreed to certain standards.
One was the format of the hang tag - blue and marked with the international handicapped symbol, readily visible from outside of the car. Most states use hang tags to be displayed hanging from the mirror when in use. Some states do allow the hang tag to be displayed by laying it on the dashboard instead (some people have difficulty reaching up to place it on and off the mirror).
The tag also has to have some way to positively identify the person it was issued to. Different states handle this in different ways, but it needs to be able to be traced back to the person it was issued to.
I have never heard of stickers issued by states for handicapped parking permits, but companies/schools sometimes use them in addition to a state issued handicapped parking permit.
As far as I know, all states will issue either one handicapped license plate and one handicapped hang tag OR 2 handicapped hang tags. I believe in all states that a handicapped license plate will only be issued if the registered owner of the vehicle is disabled or is the parent of a disabled minor child who qualifies for handicapped paking.
The hang tag in addition to license plate or second hang tag solves the problem of travel.
If we can't get someone to drive us to the airport from home, we park our ramp equipped van in a handicapped spot, using one of our DD's handicapped hang tags. We bring the other one with us when we rent a car or van so that we can use that hang tag to legally park in handicapped parking spots in Florida.
People who are issued handicapped parking permits know its not allowed to park in those spots without a permit, so if they do, they should realize there will be a penalty. I know that if I forget to put DD's hang tag up when parking to take her some place, I could get a ticket.