CRM API Search Record for Last Name equals "."

CRM API Search Record for Last Name equals "."

When using the CRM API to look for all contacts with a lastname = "." The API returns an Invalid Query Reponse

I have tried

  1. (Last_Name:equals:.)
  2. (Last_Name:equals:%5C.)
  3. (Last_Name:equals:\.)
We have a scenario where the Last Name may not be known for a Sales Order Quote Contact and so instead of using a word such as "unknown" which looks ugly in any output I chose to use "." 

Thanks in Advance