I am contemplating different issuance models... currently the number of unique types of shares that can be issued per chain is limited to 2^16 or about 65K.
In this sense the ability to issue shares is a limited resource. I am thinking of limiting it to one new type per block maximum and thus who ever paid the highest transaction fee would get their shares issued first.
Might be worth considering a share-name expiration time also. If someone issues the name "urple" and then never does anything with it, let it expire.
issuer.issuance.expirationdate
Luckybit.Luckyshares.09132014 for example.
I would want to be able to set my vouchers to expire at predetermined dates in some cases.
Shares are another matter, but a share can also act as a voucher.
You could come up with a ticker but internally you would want to store it differently.
If space runs out on 4 letters, just add another letter. If that doesn't work then add a dot, a date, an issuer, and so on.
That is what Counterparty intends to do.