Although i don't have answer to your question but similar question was asked in this forum. Please have a look.Hello guys I am going to sponsor my parents from India and my dad gives thumb impression and he don’t sign the documents does he need to notarized the documents or without notarized only thumb impression will be fine. Any help will be appreciated.
https://www.canadavisa.com/canada-immigration-discussion-board/threads/signature-on-trv-thumb-impression.411052/