Syntax error when querying Custom fields with Exclamation Mark via Contract-Based REST API

Question

Why some custom fields contain an exclamation mark in their name ex.: Tasks_ParentNoteID!Subject and CustomerClassRecord.LocaleName!translatedName? I'm getting the schema of custom fields of an entity using the contract-based REST API (https://help-2020r1.acumatica.com/(W(13))/Help?ScreenId=ShowWiki&pageid=64daacf1-75c4-4bfa-b57b-36222020e7c9).

The URL I'm using is as below:

GET /entity/DefaultExt/17.200.001/Contact/$adHocSchema

The sample from the JSON response is as below:

"custom": {
        "Contact": {
            "ContactID!displayName": {
                "type": "CustomStringField",
                "value": null
            },
            "NoteText": {
                "type": "CustomStringField",
                "value": null
            },
            "NoteID": {
                "type": "CustomGuidField",
                "value": null
            }
        },
        "ContactCurrent2": { .......

How do I query this fields using the contract-based REST API since using the exact name:

GET /entity/DefaultExt/17.200.001/Contact?$skip=0&$top=1000&$Custom=Contact.ContactID!displayName

I get the error message:

exceptionMessage=Syntax error: character '!' is not valid at position 17 in 'Contact.ContactID!displayName'.