The software doesn't write any markers to the container file without the user's permission.
Markers help to identify the file format based on its contents.
No marker available means no one is able to prove (without the password) that the container is a Cryptic Disk one - that it contains encrypted data. The file contents look like a random set of data.
Don't know the exact size for your encrypted container? No problem!
Use the "Expandable file size" option. The software adjusts the container file size as you add data to it.