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
