It is likely that the symbols refer to settings for the brush height, to allow for the vacuum being used on a range of flooring, from bare vinyl, parquet or laminate, etc., through short pile carpet and all the way up to shag pile (oooer missus).
You will have doubtless already have done the obvious and have searched for, and found, the manual that explains it all but, just on case not: https://www.hoover.co.uk/en_GB/search-for-manual
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