Please add the Key Prefix to (Custom) Object's Detail Page. You could put it right under the API Name. It'd be helpful to have the Key Prefix so to quickly access the Object's List Views even if there isn't a Tab for the Object.
: On the Object Detail Page, directly provide the link to its List Views.
: List Views are located at https://mydomain.my.salesforce.com/[Key Prefix]
: Use the following in Execute Anonymous:
System.debug('keyPrefix: ' + My_Object__c.SObjectType.getDescribe().getKeyPrefix());