From election department website
Step 6 - Inside The Booth, Mark Your Choice On The Ballot
Paper
DO mark your choice CLEARLY with an X in the box-space on the
right-hand side, opposite the name and symbol of the candidate or
candidates of your choice.
DON'T sign or make any marks on the ballot paper that may identify
you.
DON'T show your ballot paper to anyone else in the polling
station.
In another page
Mark your choice on your ballot paper clearly. Choose only
one.
There is no mention that tick or turtle cannot, just make sure you
are not identifiable with turtle 
