As a minor change to @PeterClemmensen's solution I would suggest:
data want;
set have;
burberry_bought = (index(UPCASE(brand), 'BURBERRY')) > 0;
valentino_bought = index(UPCASE(brand), 'VALENTINO') > 0;
run;
This will assign values of 1 for true and 0 for false. If you really need to show text Yes/No then a custom format can be assigned. The 1/0 coding lends itself to summaries much better as the SUM of the bought variable will be the total times bought, the MEAN will be a percentage in decimal form. Also if you actual data has one field with potentially multiple entries, such as "burberry valentino", extending this approach allows you to sum the variables within a record to know how many brands were bought.
The UPCASE and change in case to the value searched will help in case your data entry has values like Burberry, burBerry and other similar changes is letter case. Since your example data had two different values involving VALENTINO this seems a likely concern.
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