Neither are listed on the latest solent & approaches chart (latest copy just arrived today!), are they by any chance temp. marks? If so, someone will need to record Lat / Long as they go past, or contact whoever laid them...
I'm assuming its still there, the marks are from the East Cowes SC/Westerly Owners race instructions for a race this weekend.
Its a RTIR but these are from the alternative inshore course; with the forecast as it is probably wont matter