Brian Broughman (Indiana-Bloomington) & Robert Cooter (UC-Berkeley) have published Charitable Donations Fund Social Goods That the State and Markets Undersupply, 43 U. Mich. J.L. Reform 871 (2010). Here is the abstract:

Despite widespread belief in the importance of private charity, most Americans donate little or nothing. Experiments in behavioral economics show that anonymity, not human nature, causes low contributions. Anonymity poses a particular challenge for charity because of the special character of the obligation. Charity is a disjunctive social norm, meaning the obligation is owed to "A or B or C or . . . ." Disclosure of each individual's aggregate conduct is necessary for the effectiveness of any disjunctive social norm. To revitalize charity we propose a public registry where each taxpayer can voluntarily disclose the ratio between his charitable giving and income. The registry will clarify the social norm and increase average donations. We extend our analysis to pro bono legal services where a similar registry would encourage attorneys to volunteer.