You can sign the Royal Family's online book for condolence by following this link:
https://www.royal.uk/send-message-condolence and entering your message. This is a fitting tribute for Her Majesty for those who are unable to sign at a council office/condolence centre, church, Consulate/Embassy/High Commission.
It is free, easy, quick and, above all, a touching moment to know you have said your goodbyes to our longest reigning monarch.
In addition to this, there will be a 60 second silence at 2000h on Sunday preceding the State Funeral.